It's too hard to decide, with one, there is usually another. For example, if you are playing as a thief you might want to have a few illusion spells handy in case you find yourself in a tough situation.
And if you are playing as a mage it's sort of hard to JUST use magic, usually a mage (a smart one at least) will carry with him/her a shortsword or a dagger in case of a magic resistant beast or maybe, embarrassingly, they ran out of Magicka.
So yeah, no vote for me. But I do like playing as a thief or/and an assassin.
-Liam