Hardest at my school:
APUSH - the class was very hard, there was so much work, and there was so much memorization to do! However, the actual AP test was easy. All that work must have over-prepared us.
Physics - I haven't taken it, but I have heard it is the hardest class in our whole school.
Easiest at my school:
Chem - Our teacher is very good, but also extremely nice and laid back. It is not hard to get an A+. Since I'm currently taking it, I haven't taken the real AP test yet, but his students' average score is very good (I forgot what it is though).
Euro - It is a lot of work (not as much as APUSH though), but the class and test were easy.