I just looked over and asked my 14 year old his opinion: "The
Polynesian because it's cool. "Why is it cool?" "Cause it is." I thought I'd try a diversion question: "Why not the
Grand Floridian or the
Contemporary?" "Because I don't like them very much." Hmm, 14 year olds. By the way, his brothers (8 & 11) shared with me they also like the Polynesian the best, too.
Have you explored the resorts to look at their styles? I included links to the resorts to help you do that.
I would probably agree with them about the Polynesian. My sons enjoy the animal watching since many birds and bunnies are always outside the patio door, the volcano pool that plays music under the water, playing on the beach, watching the fireworks while swimming, and the incredibly easy access to both the Magic Kingdom and Epcot. I think they find the Grand Floridian a bit too feminine and the Contemporary a little less "Disneyish" even with the incredible views. Also, the Contemporary has some construction going on nearby, so I'd want to avoid that. By the way, all 3 resorts have fabulous views of the Magic Kingdom and fireworks. The Contempory's views are more spacious since the rooms are higher up while the Polynesian and Grand Floridians are more cozy and can be near the water.
With that said, don't hesitate to include visits to the other Magic Kingdom resorts (including the Wilderness Lodge; it doesn't really have MK views, though) for dining. It will give you a chance to explore them and maybe you'll decide to try a different resort for a future trip!