Which alternate upgrade for Inferno do you like the most?

Against the academic, I think it's better to use new imps. He'll have a minimum of 200 mana in the final battle – you need 800 imps to drain it all. So, in my opinion, it's better to forget about mana and use imps purely as melee fighters; with tactics and boots that give +1 to speed, they can reach the opponent.