Poly is always our first choice. It's beautiful, relaxing, quiet, and clean. Not to say the other two are not (OBVIOUSLY the GF is gorgeous) but Poly's theme really appeals to us. The water slide is super fun for all ages, the pools are wonderful, and the hot tub is great and has a lovely view to enjoy while you relax. We stay in Pago Pago (one of the buildings) quite often and we love that it's right next to the TTC to hop on the monorail for Epcot. The rooms are spacious and carry out that relaxing theme that feels nice after a really long day at the parks.
That being said, you really can't go wrong with any of them. The Contemporary would be our last choice, but that's just us. Have a wonderful trip!!