Mrs. 1000th_Guest says "Boarwalk, Boardwalk, BOARDWALK!" We are going in December; she is greatly disappointed that we aren't staying there. (We are DVC members and, when we tried to book, couldn't get a room there -- we'll be staying at Wilderness Villas this time).
We have never stayed in the Contemporary; the comments in earlier posts reflect what I have read in the past. It is also supposed to be a fairly short walk (<15 minutes) to MK. I prefer to walk from MGM to Boardwalk to avoid the transportation hassles; I suspect the same would be true with this walk.
Boardwalk is a great place to stay. The comments about the boat rides and walks to EPCOT and MGM are exactly right. The potential downside is the nighttime activity. Depending on your room, you could get a fair amount of noise.
Our first stay at Boardwalk we got a room looking over the big pool with the Kiester Coaster -- in fact when we looked out our window we saw the backsides of the people sliding down the slide. We got our room changed and got a very quiet room looking towards MGM studios -- we could see some of the Fantasmic! fireworks every night.
Last time (in January) we got a "standard view" room. It looked out onto the (front) parking lot. We had a very nice view of EPCOT fireworks every night.
We are hooked on certain goodies from the Boardwalk Bakery. I shudder to think how much we spent on Banana Cream tarts and Giant Rice Crispie Treats. My wife is disappointed that I WILL NOT take a trip every night to Boardwalk Bakery to get our nightly goodies. I must find some way to appease her.
We stayed at the Poly one night (we visit during winter and book an extra night in advance for "weather-releated delays" -- if we don't get delayed we get an extra day at the parks) on our last visit. We really liked the room and view of the Seven Seas Lagoon and MK. The restaurants were very crowded, even for off-season. We *loved* the breakfast buffet.
I don't think you can go wrong at any of these resorts.