I'm only in AB Calc, but ignoring the schedule so I can take the BC AP exam. Unfortunately, I'm WAYY behind (stupid robot) - I'm only on e^x stuff.
For most fun, I'd have to say Algebra II, mostly because of the other people in the class. I got a TI-89 in eighth grade (placed 157 in Mathcounts), and used it for half the year. Early in second semester, the other students complained that my curve-setting was caused by my calculator. The teacher (who disagreed) went along with them and let me borrow his 83 for the tests. Yes, my scores dropped, but only by 2%. I no longer set the curves, but I was usually the second-highest.
Also, the other Algebra II classes had bad teachers, and the tests were the same. Thus, they were curved, and I ended up getting 116% on the final exam!
I'm also fond of calculus, because it's so obviously useful!