I personally don't reccomend AP Bio if you haven't taken reg bio at first, and most schools have it this way. Also, I think chem would help a bit too, but then again, I think maybe I should have taken chem, bio, and physics at the same time as they very much inter-twine with each other.
If you take bio then AP, passing the AP exam should be relativley easy.
IMO, the AP Bio exam was easy, tho I wish I would have scored higher. Only got a 3 (prob due to essay portion). Also got a 3 on AP eng 1, but didn't pass the AP US history....AP US History is like the hardest exam to pass.
edit: Oh, and if you are taking an AP class just for the extra gpa point thingy; don't. It's really a silly reason to take the class just for your gpa. GPA isn't the whole point of highschool, although a lot of college's aceptance rubrics may make you feel otherwise.