Congrats to you! What a wonderfully hard decision to have to make.
We have stayed at both hotels. The Contemporary we had club level, the Poly no club level. Here is my opinion on it. I think you are going to get excellent service and offerings at both hotels. Foods offering will vary to keep with the hotel theme and feel. What it really comes down to is your personal style.
The Contemporary has a modern, sleek design and ambiance. Lots of metals and modern designs mixed with sheik colors and rich woods. If you stay in the main building, everything is close to you, food, characters, pool, excellent dining. Plus you are with in walking distance to MK! The only drawback, at least for us, was the 7am dance party at Chef Mickey's. We happened to be on that side of the hotel and the noise was noticeable if you were trying to sleep in.
The Polynesian is a world away. You actually feel like you are in a completely different place. The grounds are full of lush gardens, waterfalls, lizards and birds. Each longhouse has pluses and minuses depending on where you want to frequent such as Epcot, Grand Floridian, Great Ceremony House or the pool (two pools, quiet and AWESOME volcano pool). I have not been in the remodeled rooms yet (91 days and counting) but appear to be brightened up and more modern feel. Everyone says "Aloha". No one seems to be in a hurry, after all you are on island time.
The restaurants are wonderfully inviting. Ohana's is great for breakfast and dinner. Breakfast has characters. Plus they have PINEAPPLE DOLE WHIP at Captain Cooks! OH BABY!
Hope that helps!