I don't really care what I kill - as long as I get nice loot from it but if there is 1 task where I go "oo yay" at, it would probably be abby demons or Any strykewyrm
I would have to say, aberrant spectres, always bring a macaw for them . Steel dragons also have alot of rune bolt, limb and knive drops. They are decent. But my most favourite would be goblins.