Remember, you will be taking the "new" MCAT after 2015. That means that you will need more social science. If you feel like the AP psych will do it for you, than go for it. Otherwise, it may be good to do your psych in college closer to your date with the MCAT.
Either class will be a good class, IF the teacher is any good at what they do. A&P requires a lot of memorization. The more times you do it, the better things stick in your head. Are there dissections involved? Do they field trip to a college for "cadaver lab?"
Psych is a lot more "thinking" with some memorization thrown in.
Talk to current seniors and ask about the teachers. Not if they like the teachers, but if they LEARN from them. Sometimes the teachers that you learn the most from are the ones that most students don't like. Mostly because they make you work so dang hard. A lot of people don't like to do that so they say that they don't like the teacher.
Good luck with the choice. I know for me, I would choose A&P if there were dissections and a cadaver trip.