My favorites were definitely foreign language classes. I took French and Latin in high school (quote the teacher, who was the same for both: "are you sadistic or masochistic?" because I ended up taking both one semester lol), and German for like two semesters of college, and I took to both of those really well. Learning languages intrigues me like not much else does.
Least favorite...hmm, maybe either us government classes (ugh), or higher forms of math. I just don't "get" math. I'm still surprised I passed calculus as well as I did, because I just could not grasp it as well as I could.
(Bit of a story regarding the math bit, though. That same French/Latin teacher once asked me if I was any good at math, since she'd noticed I'd picked up on learning the languages well enough and I guess there was some kind of link between those skills? Seriously, I'd be reading books in class because I was done with my work way ahead of others. I had to say no, I wasn't - although I didn't realize until years later that I'm no good at higher math, but I'm still pretty good with arithmetic!)