Originally Posted by
Cirque
Depends on what kind of raiding you want.
From the top of my head, in cutting edge progress, currently hunters, warriors, death knight and resto druids are in a bad spot. Death knights do okay-ish now because of their festerblight crap, but other than that they don't really compare to rogues. Warlocks and moonkins are always wanted, especially warlocks, and mages are desirable as well. Resto shaman are mana batteries at best and useless at worst, so a 25 raid usually brings like 1 resto shaman for this, and 10mans will avoid them. Rdruids are avoided in general.
Tankwise, death knights are in a very sore spot, with prot paladins at the top. Most 25 mans will prefer 2 protdins, even 10 would if that won't give gearing issues.
But again, this is 'cutting edge'. The majority of heroic guilds that progress slowly but surely will pretty much take anything in any combination, because at that level, class balance is actually really decent. At that point what matters most is individual skill, which will vary widely between raiders. At top end raiding, where individual skill is equal between all raiders, the above differences really show.