AP saddles are ok if you want to do a bit of everything at low levels. They're no good for jumping if you want to be jumping big courses, no good for dressage if you want to get a correct position and start working on more advanced work etc.
If you want to do just dressage, I'd get a dressage saddle to do so. A dressage saddle is designed to help you get a good solid dressage position, with your leg under your body and a deep seat. An AP sets your leg forward, so you are almost in a chair seat and you will have to work doubly as hard to get your leg back. Doing dressage, the last thing you want to think about is trying to force your leg back all the time!