Acapulco or Puerto Vallarta?

I'm trying to plan an affordable Mexican vacation this summer. Due to summer school, we can only go in August. However, I hear its rainy season and Im afraid it will ruin our trip. Acapulco and Puerto Vallarta are affordable, (app 1,300 including plane and hotel for 2) and dont seem to be as commercial as Cancun and Playa del Carmen. Which one would you choose? Any suggestions will be greatly welcomed!