The way I've done it:
Mage:
Air staff @ trolls -> Mindspike (5) @ trolls/catcomb roaches -> Batwing Wand/orb (30) @ hobgoblins(semi afk with high def)/hill giants/outlaws -> Splitbark (40) @ hobgoblins/hill giants/outlaws + Dungeoneering -> Nature staff (53) @ Ankous/Lesser demons/Greater demons. Only upgrade to Gravites once get into things like Mole, not a necessity though.
Ranged and melee should have a similar path but you can make weapon upgrade much more frequently. Using Melee AoE abilities at outlaws can give over 60k xp/h + tarromin herbs for magic potions
Hope that helps