Art, high school. It could've been partially due to the fact that I had a repressed crush on my teacher. (he was fun, cute, completely insane, and he once drew an impromptu picture of me and confided to me that I was his favorite student, even though I was one of the quietest. hmm, Kinda creepy)
But I think it was mainly due to the comfortable environment, the group critiques (why can't every class have that?), and the freedom to progress as much or as little as you wanted. Also, I'm pretty creative and it was a refreshing change from keyboarding or pre-calc or whatever happened to precede the class.
Oh oh, and printmaking might've been the best. Partially due to the incredible medium, partially due to my classmates. There were only two other students. One was Ron Gardenhire's daughter, incidentally. She was completely out of her mind but pretty amusing, might've been on something. Another was this awesome freshman who looked and talked exactly like Dr. Strangelove...except with a bowl haircut and an inexplicable obsession with tractors. He wasn't considered remotely popular or "cool", but I have no idea why. How does someone like that slip under everyone's radar? wtf is wrong with people.