I was just wondering your opinions.

Illusion for both

Illusion is most fun for me because If I make a extremely powerful potion, I can calm or anger any NPC.

Illusion is the most useful because I can get out of danger and cause hostiles to attack eachother.

I don't really have a favorite school, but if I had to choose one, it would be Conjuration.

As for the most useful, I always find Restoration to help me out when I need it the most. It can restore your Health and Stamina.

Restoration is most useful for my current no-potion game, but conjuration is probably the best overall (a good potion supply makes restoration kind of redundant).

Destruction is just too much fun.

For me it's conjuration due to how helpful it can be when the numbers aren't to my liking.

Alteration is pretty fun too, love the underwater breathing spell.

Restoration is the most versatile and synergizes well with most builds in my opinion. Once you get the Respite perk, it gives fighters some pretty good incentive, and it's good to fall back on when potions are low.

I do really like the perks for restoration. Like the one with more magic regen and 50% more health from spells, but the only useful spells are the healing ones.