Yeah, AS exams have been alright for me - mainly because I like them. Hell I didn't revise for politics but it's the simple fact I like the subject and learn most of the terms etc in the class that make me do alright. Chemistry I hated back in year 9 - dropped it after a year, all I did was put my finger under the taps and turn it on, creating a cool, distratcing squirty effect at the table infront (one time we had some major water fight on it, and it went on the projector and yeah... didn't go down too well with the teacher lol).
But yeah seriously, take subjects you enjoy doing - it makes college so much more enjoyable and easier.