I have stayed at the Bay Lake Tower last year, and actually have a vacation planned for the Polynesian. Our experience at the BLT was not very good. It was a nice hotel, but there were a series of problems. The room was dirty when we arrived and the couch in the room had a torn hole in it?? Pumpkin seeds under the sitting the chair?
In addition, the emergency sprinkler in our room was having problems. They had to move us over to the Contemporary for a few nights because they were booked solid. I just expected more for it being a newer hotel.
Obviously I wouldn't expect this to happen every time and I am not opposed to going back to the BLT, but I am very excited to try the Polynesian. I do agree with the previous poster that is the "modern" looking hotel vs. the tropical theme. Definitely more "to see" at the Polynesian, but BLT was a neat look too.
A real nice thing for the BLT is that it is a short walk to the front gate of Magic Kingdom. For kids, this is a nice thing. The pool is only accessible by BLT occupants too. I'm hoping for a great experience at the Polynesian and am looking forward to it.