I would say:
Aquatica: For the atmosphere and attractions that will appeal to different people (e.g. some wilder slides and also plenty of things that will appeal to visitors that don't care for wild slides and would rather just chill, enjoy the wave pool etc.)
Wet n Wild: More intense slides/rides and lots of family/team rides.
So my choice would depend on whether all of you enjoy going on "wilder" slides (Wet n Wild) or whether some of you are a bit more hesitant (Aquatica). Both are great water parks though.
Also, I had the impression that there were more locals at Wet n Wild so it seemed more crowded (on a summer weekend).