Saffron wrote:There's no easy or 100% right way of answering this. However, it's true that most people of a class would play the same spec for raids. There were off spec raiders for various reasons, but generally, if you want to get into a guild for a trial, you may be best off using these...
Paladin - Holy. Very good raid healers and providers of buffs. Not a pro on these since I played horde, but I think maybe some guilds ran with one Retribution paladin. I think Prot paladins had awful mana issues.
Shaman - Restoration. Outstanding group healers.
Basically, if your chosen class has a healing spec, you're expected to play it most of the time.
Just going to add on to what Saffron said...
Holy Paladins are the best healers in terms of mana efficiency. You can literally spam Flash of Light for days.
Retribution paladins were usually brought to keep up a judgement on the target while using Nightfall (crafted weapon that does +15% spell damage taken debuff). Are they really worth bringing over a primary DPS like a rogue or warrior, no. Holy Paladins can keep judgements up and you can have an offtank use Nightfall when they aren't tanking an add and get the same results while getting an overall damage increase because retribution paladin DPS is sub-par until Naxxramas when Exorcism can be added into the rotation. People will probably argue and link stats of high dps retribution paladins, but there is usually a gear disparity involved. A BIS raid gear ret paladin will out dps a blue geared rogue or warrior. At even gear levels though, the paladin will always be behind.
Protection paladins... where do I start. This fascination of protection paladins came about from BC onward and has been assumed they can do the same in Vanilla. In Vanilla, they DO NOT HAVE TAUNT. Simply put, if they lose threat, you're screwed. They do not have any cooldowns other than Lay on Hands, which is an hour cooldown and makes them lose all there mana (which is how they generate threat). On Nostalrius, mobs that are CC'ed with sheeps and what not still have a threat generation table. Healers will always be on top of the threat meters for bosses such as Majordomo. With the lack of taunt, protection paladins are absolutely worthless other than tanking the first mob that gets killed, since Majordomo drops threat as well. When it comes down to it, can protection paladins tank? Yes. Can feral druids and warriors tank better? Absolutely.
Restoration Shamans... simply put the best raid healers on Horde side. Chain heal is so powerful. Not much else to be said about them, they are an absolute necessity.
Enhancement Shamans are similar to Retribution Paladins in the aspect they bring utility to a melee group as well as function as the Nightfall debuffer (15% spell damage debuff). Once again, like Retribution Paladins, their dps is sub-par and it's better to bring a rogue or warrior and have the off-tank(s) use Nightfall. Can you use them? Yes. Once again though you have to ask yourself, is it worth it to bring one over a rogue or warrior? Not really.
Elemental Shamans, simply put they have no raid utility and their damage will always be pretty low. They just weren't designed correctly for PVE until Burning Crusade. For instance, on Garr, they literally cannot damage anything because Earth Elementals are immune to Nature damage (Lightning Bolt + Chain Lightning). Worth bringing? No.