Imo,as Aslan said:
1) hunter (strong pet,movement speed with aspect)
2) lock (pet,can wand if mana pbm,no need to drink with life tap)
3) druid (feral spec imo not as strong as pet classes,but very fast levelling)
4) rogue (vanish save life and time,best dmg for no cost)
5) mage (water summon,blink,even without aoe its ok)
6) shamans (ghost form help a lot,but need so much mana to do dmg)
7) priest (heal and wand,but walk during hours)
8) paladin (not very hard cause u never die,but mobs u need so much time to kill...)
9) warriors (hardcore class. If u never played vanilla/bc,u will understand after u first met a 2-group mobs)