Paladins are tanks, mages are nice because they dont need food or water, shamans can heal and do decent dps, druids are good for the same reasons.
Daily Quest (and every 10th level). 50% exp Buff reward. But only lasts 1 hour. Monk as Brewmaster. Easy as hell. Kills 4-5 Mobs (lvl 60) without taking any damage thanks "Guard".
Last time I played a mage (long ago) they constantly needed water. Is this not the case anymore? Enchancement Shamans are just fun.
Although people seem to say that priests are bad, my Spriest has had no problems running with just the 272 gear. It has had just as easy/easier time than my pally.
I wonder no one mentioned DK Start at lvl55 and whack your way to 90 in almost no time (Frost 2H -> undefeatable!) plus they are fun to play again since MoP.
From the little experience I have had botting - I would say Hunter / DK have been my choice. My rogue has been a bloody nightmare!