Lacks simplicity BUT

1-4
Paladin - Tank
Druid - Heals - (I like rolling instant cast hots more than 2.5 sec heals, plus hybrid ability to change to boomkin or tank if needed.)
Priest - Castsequence macros work fine for this, adds utility, PW:F, +shadow damage, mana regen, passive healing, etc)
Warlock - Castsequence macros work fine for dps, compliments shadow priest, dot, dot dor, bloodpact, healthstone, soulstone, offtank if needed with voidwalker

5th
Shaman if you wanna be really divers. Totems ftw, chainheal is nice, not another clothy so can take a hit or two.
Mage provides good dps, AOE, and free drinks
Warlock - shadow damage ftw, simplicity of not having yet a 5th class.