Skills for an Inferno hero.

I always choose Gate Opening, Attack, Chaos Magic, Luck, and Leadership.
Gate Opening is definitely a plus for Inferno. Once, I played a local multiplayer game with a friend on Legions (we developed for a long time, and the number of even level 7 units was no less than 1000!!!!!!!). He was playing as Sylvan, but he had a much larger army than me. However, Gate Opening changed the situation: after opening the gate, 1800 more of the same fire demons appeared, in addition to the 3000 fire demons already there!! It's very useful.