Skills for an Inferno hero.

I don't like Dark and Light magic in the early levels; when you max out your spellcasting skills, you won't even remember those spells. Although, 4-5 spells from Dark magic are very dangerous, and Light magic only becomes frequently used at level 5.

As for Chaos magic, it should be used like this: take a Fire Lord, attack with Fireball, reduce defense (with Fire Lord), and then hit with all your might using Hellfire; only ashes will remain.
And when playing as Marbas, you can just obliterate everything with Armageddon.