I like all of the monorail resorts - a little unhelpful, perhaps.

But we have stayed at the Polynesian most out of the three.
What I love about each:
Polynesian:
- atmosphere is amazing. I love the torches at night, love the smell, love the volcano pool and the lagoon, the GCH, smores on the beach, fireworks from the beach (when they exist, of course)
- love the food options. I am not a coffee drinker (except iced), but my husband is and they have especially good coffee here. I DO love the dole whips. Ohana is here, which is a lot of fun. We have never done the luau somehow, but it is so much fun that it is right on site. Kona Cafe or Captain Cooks for a quicker fix of tonga toast or bread pudding is lots of fun. Plus an easy walk to GF for our beloved V&A.
- honestly have never had a bad view here. We have mostly stayed in Samoa, once in Hawaii, and family have stayed in I believe Rarotonga and Aotearoa. All lovely and large rooms with nice views of gardens, pool or monorail.
- transportation. When it is running, the easy access to the epcot monorail letting you access two parks by monorail is such a bonus. This is one of the major reasons we chose Poly so many times, plus everything listed above.
Contemporary (and BLT)
- convenience. The added convenience of that quick walk to MK was so appreciated every time we walked there or back, especially leaving a crowded park at night or with a cranky child.
- food choices. The Wave is underrated, I think. Views from California Grill are of course wonderful. Note that the Wave is closing for a refurb.
- the rooms! I really like the rooms at CR, and I LOVE the 1 bedrooms at BLT. With 2 teens, you may want to look into those. Having 2 bathrooms and a washer/dryer was so nice, plus we made some use of the kitchen. We ordered a pizza one night, as I recall. Renting points may be a better choice in terms of saving money, but look into insurance if you do that in case you have to cancel the reservation.
- the monorail! Sorry. The monorail going through the hotel is just cool. I always thought this hotel was amazing when I was little, and I still really like it.
Grand Floridian
- AMAZING food. We LOVE Victoria & Albert's. We have eaten here on every trip. I know it is closed now, and your kids may not care at all for it, but my husband and I adore it. The food and staff are amazing. There are also some other wonderful food options here. We have really enjoyed Narcoossee's, as well, but haven't yet had a chance to try Citrico's.
- Walk to MK. It is a longer walk, but you can still do it, especially if the weather is not oppressive during the time of year of your visit. It can be a pleasant start or end to your day.
- Views. Really nice views from almost all rooms.
I don't think there is a bad choice with the monorail hotels. It is just a matter of which theme you like best and what you want to be closest to/have better access to. Each of these hotels is of course a quick monorail ride or walk from the other, so you can still enjoy so much of what the others have to offer. Have a wonderful trip!