Power and Durability and flexibility in multiple aspects.
Dogpoo : can easily melt anything he touches, can also be used as a flanker for some serious damage. Good off tank.
Heidi : cheap good stats, off tank.
butters : high damage easy to level, deathwish can speed up an ally for a quick kill.
Cartman : easy tank with aoe and anti-swarm capability
Stan : good CC, quick movement, and medium damage make for a good support
Jimmy ADV: good tank support, high damage, and great debuff
Jimmy SCI : quick cast low cost good stats with an ability lock aura
Timmy : long range knock back with small aoe burst damage
Clyde : ability to nearly instantly kill any target. Good quick counter, high damage good health decent speed.
Wendy : light costing ranged character with a powerful special that hits three targets for decent damage.
Arrowstorm : immergency contigiency that can quickly turn the tyde of battle, isntantly kill rogues, dougies, and low hp enemies all over the map.
Nelly (actually PC principal) : high hp, knockback for cc, and can push a line back to enemy players area easily.