That depends largely on what portion of school you mean. In high school I would have to say it was science or more particularly genetics. Now don't go getting all impressed, the subject of genetics just clicked. Right from the start I could completely understand it as it were as simple as riding a bike. I am sure everyone experiences this from time to time.
In college I still liked genetics but since it was my focus I felt I could then direct my spare energy into fun stuff. In so doing I came across a floral design class that I just fell in love with. Once again don't go getting some funky idea that I was some great floral design prodigy. To be honest I was no more than average, but it was nice to have an outlet that was purely fun.