Below are, in order, the sides that have taken first place in an official tournament. Many of these sides were around long before they won; the version described is the one that became champion.
Hardcoded Predator Edit
In the early days, when sides were written in C++ and built into the engine, the best of them was Predator. It was a simple gatherer with blasters and heavy armor. It won consistently, despite a serious friendly-fire problem, because there was nothing else that could both eat and fight.
After the hardcoded sides stopped working, there was a recreated Predator with (inaccurate) grenades. I think it was the best side for a while, for the same reason.
It's dangerous to go too far from home - you might get shot at. Gatherers have a problem with this. So Warren wrote a side whose gatherers prefer food that's close to their birthplaces. They also make stationary grenade launchers to fortify territory. This combination of caution and expansion made Homesick the first champion worth the title.
Old fighting Rat Edit
Once upon a time, it was possible to fire a weapon even when you had shields up. Rat was the first side to take advantage of this. (Actually, there was a hardcoded side called Leech that used blasters and syphons while shielded, but I don't think it was ever finished enough to be effective.) It ignored enemies and blindly gathered food, raising a shield when shot at and only shooting back when its food-gathering brought it close to a target. With the advantage of shields, this was good enough to give it scores of over 70%.
Rat made us think about the roles we wanted for shields, and after some confusion, we changed them so weapons no longer worked. So Warren split Rat into two sides: the modern Rat, which uses shields but has no weapon, and Rat-without-shields, which abandoned the shield but kept weapon and championship.
Rat without shields Edit
Shields weren't the only reason for Rat's success, and this version held on to the championship (narrowly). It had a high repair rate, which in combination with heavy armor (instead of shields) kept it alive despite its nearsightedness. It had enough armament to win most battles, and its mobility (in pursuit of food) gave it a good chance of eliminating most enemies, or at least surviving.
Megadont exploited several imbalances and a common weakness of its enemies. It consisted of one huge cell with range-40 grenades. It had a constructor, but that was a waste of energy, as in practice it never reproduced. Its size gave it an advantage in combat. Large grenades were too powerful, and long range too cheap, so it exploited these. More important, it exploited its enemies' indifference to attack: most sides at the time made no attempt to defend themselves unless they could see an enemy robot. Megadont won by killing everything else from long range.
Fixing the grenade size and range imbalances weakened Megadont. The arrival of a side which did not ignore bombardment defeated it.
Life and Death Edit
Life and Death was designed specifically to beat Megadont. It was the first side to chase shots, and therefore the first that could resist Megadont's long-range bombardment. Like Gnats, it uses a syphon and short-range blaster to stun and kill its enemies. It also has an unarmed type which is supposed to survive when it loses battles. It beat Megadont (and everything else) surprisingly easily.
Later versions zigzag while charging, use shields, and eat while fighting.
Teledont was champion for a long time. It's like Megadont, but with a blaster with a damage rate higher than that of Megadont's grenade launcher. It defeats Life and Death by storing enough energy to delay stunning by syphons. It reproduces, and avoids friendly fire by sending its cells to different parts of the world.
Teledont won as long as nothing could kill it, but it grows so slowly that it dies if it ever meets serious resistance. In the presence of opponents that chase shots, it picks more fights than it can handle and dies quickly.
Version 5 makes the first use of multiple sensor returns, to select food and targets better. Version 6f briefly recovered the championship in the days of Intoxicated. We're not sure why.
Eventually was the first side to change its strategy over time: it devotes energy to growth (and defense, in later versions) at first, and later switches to offense. This gives it faster growth than most opponents, so its offense can overwhelm them. The offense is only a lot of simple missiles, but that's more offense than most sides have, and more than any side at the time could resist. Even sides that could shoot down almost all the missiles eventually missed a few. Eventually won by elimination more than half the time, until Productive 3 came along and did the same thing better. Versions 4 and later ignore Productive's decoys. Version 7 was a disaster, with a doubletime over 4000, and fell to third place; version 8 fixed this. Later versions coordinate their missiles in an effort to find targets faster and overwhelm their defenses.
Productive (Bombs and Factories) Edit
The first version of Productive was helpless - no wonder; it was the author's first side! (Seeing it not working made Devon write Eventually.) The second version was the first side to move deliberately: it goes to the nearest corner, where wandering enemies are less likely to find it. It tends to get killed by blundering into an enemy, but this is more than made up for by the safety of the corner. Some versions also communicate to arrange some of the cells in a line (to reduce traffic jams and vulnerability to missile accidents) and to disperse the missiles. The third version was the first side to have an effective defense against missiles: it uses tiny, cheap missiles as decoys and antimissiles. The combination of hiding in a corner, offense, and missile defense works pretty well, even after missiles were weakened.
World Toad Edit
Written to exploit the size advantage, World Toad is a giant gatherer with a lot of attention to combat. It doesn't fight unnecessarily, and has good defense, so it used to survive more than half the time. Because it chases shots, it resists long-range attacks (it was designed with Teledont in mind) and tends to kill sides that use them. This has a substantial effect on game balance.
Most of the earlier champions often won by elimination, but World Toad rarely did. It was good at combat, but it didn't try to attack; its strength was in survival.
Few sides have good defense, so Intoxicated could often straightforwardly kill them all. It has passive dodging, which lets it take on large groups of enemies. It's also the first side to travel in a group. This leads to a good deal of accidental group combat.
Even after several rule changes to weaken large cells, its size helps. A large cell concentrates firepower without any coordination effort. It also reduces friendly fire. Between its size and its agressiveness, Intoxicated's success is very annoying from a game-balance standpoint. This sort of side isn't supposed to do well.
Bacteria (in a large world) Edit
This was supposed to be a clone of Microb, plus some armed types. But when I entered an incomplete version in a tournament with a 14x14 world, it won by a large margin. (This wasn't repeatable in a normal world, but it often scores well.) So I left it as is.
It has only two types: an autotroph, and a gatherer that runs away from shots. Running is a good idea for any unarmed type, but it works especially well with a trial-and-error strategy. Instead of dying, misplaced cells just run to better pastures. This works much better than shields.
Active Large Edit
Active (of any flavor) is spooky to watch. It appears to dodge shots before they're even fired, and to somehow cause enemies to shoot at places it isn't. It wins by elimination a lot, but it's hard to resent something so clever.
Active 2 doesn't work very well, because it spends half its construction on missiles, which aren't very useful in most situations. Since Active Large costs twice as much as its missiles, it accidentally spends less on missiles. This doesn't completely explain its success, though; Active 3 builds even fewer missiles, but doesn't do quite as well. Apparently size is still an advantage.
Commune is a communication-intensive side. It completely separates defense from economy, in order to concentrate as much power as possible in its fighters. Its gatherers respond to other cells' requests for energy with syphons, so other types gain the energetic benefit of gathering without having to do it themselves. (They also tend to eat all the food near the colony, so it does not attract enemy gatherers.) The fighters respond to threats as a group, so shooting at it provokes disproportionate retaliation (which is why the fighter type is called Revenge).
Because the fighters have short range, Commune is vulnerable to missiles. The separation of gestation from gathering (but not from solar power) also means it grows rather slowly.
Missile Bacteria Edit
Business Cycle uses missiles for defense, with great success. So I added some simple defensive missiles (the type took five minutes to write) to Bacteria. They chase shots, so shooting at Missile Bacteria is usually fatal.
Not Quite Harmless Edit
This uses Not Quite Wise as its economy, supporting a shielded leech type. The idea of a leech is years old, but this is the first one that works. No existing side could handle it; they either killed themselves by friendly fire or ran out of energy. It even resists missiles, thanks to its shields. It should be helpless against syphon users such as Gnats or Life and Death, though.
We let syphons work through shields to encourage leeches, even though we knew it wasn't a good idea. Stopping this weakened leeches, but they remain useful as decoys.
Revenge Killer Edit
Warren thought short-ranged blasters were overpowered, but no side was specialized to defeat them, so he wrote one. Revenge Killer keeps Revenges at arm's length by running away and pushing them with a force field, and kills them with a large blaster. It's rather agressive, so it can capture lots of territory for its skittish gatherers.
This also works well against missiles, and indeed against pretty much everything. And Warren no longer thinks short-ranged blasters are overpowered.
Later versions added food-hashing for faster growth, and abandoned the forcefield in favor of larger engines, and regained the championship in 2008.
Like Business Cycle, Untouchable collects food with force fields, without risking its gatherers. It earns its name by also using the force fields on enemies - it pushes them away, which is easier than killing them, and makes Untouchable almost impossible to attack. The first version had long-range grenades, but it was hard to coordinate these with the force fields, so they were removed in favor of medium-range passive-dodging fighters. Feeding all this takes a lot of syphons, which make the side rather pretty.
When force fields were weakened, Untouchable became easier to touch, but because of its good fighters it remains one of the best sides.
Commune Plus Edit
Commune has not changed much since the first version, because it matches Devon's vision of what it should be. But such a vision is not a reliable guide to quality, and Warren was not interested in following it. He added an autotrophic type: Solar Outlet (from Untouchable). This feeds Revenges more reliably than Sustenance, and improves the growth rate when the colony is large. Together with a few other upgrades, which will probably make their way back into Commune, this fixes many of Commune's weaknesses.
Wise Men Edit
Business Cycle's Day Trader combines gathering and fighting pretty well. Wise Men splits it into gatherers, fighters, and decoys. Version 2 won by building lots of those fighters and using them as a group. (The decoys seem to be a waste of energy; the side does better if it builds more fighters instead.)
Segregated Eaters Edit
Since the beginning, gatherers have wasted time when more than one cell tries to eat the same food. Sides which communicate about who's eating what can grow much faster. Segregated Eaters assigns each tile to a cell, intead of tracking individual foods like Frog Celestial. Also unlike Frog Celestial, it has a separate fighter type. These fighters are aggressive and numerous enough that Segregated Eaters often wins by elimination.
Move Zig! Edit
Productive, Shields + Cowards and Unproductive hide their solar cells in corners, to avoid getting attacked by wandering enemies. Move Zig! does the same, and adds fast-growing gatherers and short-range fighters to make use of the rest of the world. The combination provides good survival and a good chance of rapid growth.
The Lunacy Edit
Massive Beast is a reincarnation of Teledont: a single large cell which uses a long-range blaster to indiscriminately attack everything. As with Teledont, the effectiveness of this strategy depends on whether other sides react appropriately. Against sides that ignore shots, or that charge in a straight line and die before they get in range, it can often win by elimination. Against sides that chase shots while dodging, like Active 8, it gets killed.
Since it grows very slowly, Massive Beast works best combined with another type that grows faster. The Lunacy combines it with the previous champion, Revenge Killer 4.