The series: [Introduction, and a call for comments, Solo Difficulty vs Group Difficulty, PvE vs PvP, Variety vs Specialization, Solo Performer vs Group Utility, Your role in a PvE raid]
This is how every talent tree of every class fits into a pve raid.
This list assumes players at the same skill and gear level. Everyone knows someone who will say “how can you say that X does more damage than Y, my friend is Y and zomg pwns all in a big raid guild, blah blah”. The guild you mentioned doesn’t have the same quality at every person, your friend happens to be the best player in that guild. Your friend would probably be the best at any class they chose.
Also, many raid encounters specifically highlight one class’s feature over another. So these comparators don’t hold true for every event in the game.
Now, notice that I’m not listing every popular build. The typical hunter beastmaster build is 41/20/0 or 41 points in Beastmaster, 20 in Marksmanship, 0 in Survival. The typical combat rogue build is 40-odd points in Combat, 20 or so in Assassination. This isn’t a catalog of every build for every class, just sweeping generalizations by talent tree.
Finally, if I’ve made any errors, please leave a comment, and I’ll update this list.
Common to All roles
Druid - good general purpose raid buff, good debuffs, good caster utility with innervate, good raid utility with in-battle resurrection
Hunter - good ranged physical damage, nice variety of debuffs, best aggro management, can help manage the aggro of others, infinite duration of damage (unique for ranged classes), awkward crowd control
Mage - excellent ranged single target/aoe damage, pure damage class, caster raid buffs, decent aggro management, good crowd control, free food/drink
Paladin - excellent raid buffs via blessings, multiple paladins stack very well in raids due to wide variety of these blessings, good variety of party buffs in auras, nice buff/debuff melee option in judgments
Priest - decent raid buffs, good threat management, limited crowd control
Rogue - pure damage class, excellent single-target melee damage, good aggro management
Shaman - excellent group utility via totems
Warlock - excellent single target/aoe damage, best damage over time, good debuffs to either do damage or enhance anyone else’s, free health potion equivalent between fights, limited crowd control, good raid wipe recovery via soulstone, limited aggro management
Warrior - enhances party health or melee damage, good aoe melee debuffs
Damage / Dps
Druid (feral) - good melee physical damage, enhances raid melee damage, damage doesn’t scale through endgame due to itemization
Druid (balance) — good ranged magic damage, enhances group caster damage
Hunter (beastmaster) — excellent ranged physical damage, enhances group damage of any type
Hunter (marksman) — PvP damage spec, can also be excellent PvE damage with mid-tier raiding gear and up, good physical damage group buff
Hunter (survival) - PvP survivability/control. Also good raid utility in deep endgame PvE raiding via Expose Weakness, enhances all physical damage.
Mage (fire) — highest sustained ranged magic damage
Mage (frost) — PvP survivability/control, lowest burst damage and highest duration
Mage (arcane) — PvP burst damage, highest burst damage and lowest duration
Paladin (retribution) — PvP damage. Also excellent party damage buff in large raids.
Priest (shadow) — decent ranged magic damage, good debuffs, excellent group utility in constant mana and health regen, damage doesn’t scale throughout endgame due to itemization
Rogue (combat) — highest sustained melee physical damage
Rogue (assassination) — my wife says, “Good question, what do full assassination/mutilate rogues do that combat rogues don’t?”
Rogue (subtlety) — PvP survivability/control.
Shaman (enhancement) — good physical melee damage, greatly enhances group melee damage
Shaman (elemental) — PvP nuking.
Warlock (affliction) - excellent damage against bosses, excellent raid utility via varied mob debuffs; aggro problems due to most damage being DoT and therefore hard to slow down when problems arise.
Warlock (demonology) - good raid damage, most self-boosting abilities, versatility via different pet sacrifices
Warlock (destruction) - PvP burst damage; can be excellent in deep endgame raids with appropriate crit gear. (looking for more info)
Warrior (arms) — PvP damage; however, with sufficient physical damage support (usually in mid/deep endgame) mob debuffs enhance physical damage to make an arms warrior useful.
Warrior (fury) — good melee physical damage, good melee aoe
Deathknight - best tank for caster targets (according to current pre-expansion information)
Druid (feral) - best tank for melee targets, best single-target offtank, gear is problematic in scaling throughout endgame (also, can switch without respec to cat-dps between fights)
Paladin (protection) - best tank for multiple targets
Warrior (protection) - 2nd best at everything deathknight/druid/pally are good at, also great generic survivability tricks for boss fights
Druid (restoration) - best heals over time, best healer on the move
Paladin (holy) - best single-target healer
Priest (holy) - 2nd best at everything druid/pally/shammy are good at
Priest (discipline) - PvP healer, good raid caster buff
Shaman (restoration) - best multi-target healer