i'll see you there when i 'accidently' set a bunch of cornish pixies loose in the slytherin dorm room.
gotta love pollyjuice potion!
Herbology because I would have an amazing teacher (Longbottom) and fun teachers always make the class better no matter how good or bad it is, care for magical creatures because I love animals and thing it would be cool to work with magical ones like unicorns, and flying (must I explain why). I'd probably be looking forward to all of them, but those are some of my top ones.
Transfiguration and Charms! DADA sounds really neat and all, but I feel like Transfiguration and Charms would be the most challenging and the most fun. I'm not good at cooking, so I'd say not potions since it's so similar, and technically if I just got the letter then I can't take Ancient Runes yet ;)
Transfiguration and Defence against the dark arts
Probable DADA or Transfiguration
Charms followed by potions or transfiguration!