I think I'd most look foward to defence against the dark arts (lol i should just go ahead and say DADA) or potions myself though becoming an animagus is cool too and thats transfiguration....this question is harder than i thought... Yep D.A.D.A for me!
Portions, which is weird for a gryffindor. But I like to blend things. Also, I'm not much for wands. Much cooler to be able to produce magic without a tool... And I'm not ONLY saying that because I'm pretty sure I'd suck at wand movements... probably. xD