I'd first question how you managed to pick night elf.
Destruction svcks if you're not going to use both hands. You want the dualcast stagger perk. You'll have to spread over into something else if you're not going to make use of that, like conjuration.
Illusion is unreliable, its core abilities useless against undead and dragons that have been the majority of enemies I've faced. Restoration and alteration are defensive, so that's getting outright redundant paired with a shield.
Conjuration is the winner.