I wish I could choose two. Herbology is my numero uno because it's an interesting thing that even works in real life, imagine adding a little magic to that. I have a crap ton of old mason jars filled with some old family herbal remedies. When I'm not at work or my other job or the other job or the other job . . . my small garden is my hobby and it's like a game, trying to keep track of things, removing unwanted critters, seeing hummingbirds and bees visit. Now, if that was magic, imagine that cranked up to 100!
Transfiguration would be my second choice because it'd be a skill worth using. Travel would be easier and funner, perspectives would change and who knows when it'd become necessary to transform a rat into a coffee cup! That's called being resourceful!