I prefer Druid also. Guardian spec. Getting out of snares for free (once you get to BRD/LBRS/UBRS you will be snared endlessly), two sprints, skull bash, charge, aoe disorient and pushback. They move through the instance so fast and can swipe it all down at once (switch to cat form and pop berserk). For later instances you'll need to stay in bear form for the bigger pulls but with incarnation you can put out a ton of aoe in bear form as well. My druid is about 461 in mostly pve tanking gear and nothing is a problem 1-80, entire instance pull no problem except maybe 75+ instances but by then I have the alts following so they can complete the quests (50-75% of a level for the quests alone).

I don't do instance boosting beyond 80, in cata instances there are too many stuns, knockbacks, aoe crap to kill your alts, etc. and I know at least a 90 guardian druid cannot handle large pulls, and the xp/hour was terrible. The best method I found 80-85 was the troggs in deepholm. You can pull endlessly and they don't hit hard enough to put a dent in your no matter the size of the pull.