I think Aether should be good at least but I only leveled it to 50 or so. I stopped because I had many theorycrafts and was too lazy to test them all. You could push the leeching to some crazy levels with Haunt relic, Rattosh, Scales and Harbinger of Souls if needed.
Here’s some build by @mad_lee before the recent Aether damage buff with not crazy gear (hopefully weapon can still be vendor farmed, you can get most lev 60 relic bps if you farm totems near this level, for Magelord the transmutions seem to work) although perfect affixes. It uses 2h mace but from what I heard Fleshwarped Carbine is bis now.
I had an idea to use Aether RE conduit with Aetherfire bound to it for some more damage but didn’t test it.
Spellbinder, Level 100 (GD 1.1.9.8) - Grim Dawn Build Calculator
