Apart from theming, the two other main factors are occupancy and who is staying there.
Occupancy (from highest to lowest):Movies, Sports, Music
Who stays there:
Movies: Mixture
Music: Most school music groups stay here.
Sports: Sports teams and cheerleaders usually stay here.
The sports teams and music groups can be very large and very annoying. I've only stayed at the Music, so I can't really comment on any experiences at the others. At the Music there was a large group of ~13 year olds there while we were there. We were able to avoid them for the most part, but one day we had to deal with them while waiting for a bus (and riding the bus). Also, at night they invaded the pool and a pool full of 13 year olds is not a very enjoyable thing. Overall it wasn't too bad (we are going back there this year), but it is definitely something to consider.
-DH