I'm a long term AOE instance booster pre RAF and Pre multiboxing.

I started boosting with a Frost mage and could boost alts up to and including zf. This is a 70 frost mage with quested greens and the odd BOE blue.
I have done up to the same lvl with a 70 demo warlock using VW/Felguard and SOC.

My MAIN boosting toon is my prot pally I can boost up to and including BRD no probs with him his surviability and AOE reflective dmg is really really impressive. Plus the benifit of BOP and heaven forbid ability to res ya drones being dragged is VERY useful. Plenty of reading on www.maintankadin.com re easily obtained reflective dmg gear. First and most important is the sporegar rep shield grab that and put the biggest spike u can afford/obtain on it. Youtube prot pally AOE farming for how it is done, with the recent chagnes to my pally (patch) I am going stronger then ever with him boosting. Post 40 I usually quest as it seems to be better xp/hr I have found OR I multibox instances past this rather then having the drones dragged behind. FYI my pally tank is badge/kara geared but u can do it in lower gears just dont pull big groups over ya head that all

Edit: For tips on how to use your toons you have; start how I did: www.youtube.com , www.warcraftmovies.com etc etc, Search: X class solos X instance. Watch learn observe, go try it yourself