We've stayed at all 3 multiple times and you can not go wrong with any of them. That said- we would pick the Poly. Here are my quick thoughts on all 3.
1. WL is a lower price but the trade off is smaller rooms. The resort is beautiful. The boat to MK is nice. You must take buses (as far as WDW transportation) to the other parks from WL, but we have always found the bus service to be decent there. Sometimes, not always, buses to one or two of the parks are shared with Fort Wilderness, but we still have never had much of a problem with the buses. Everything is one building which makes it easy. Also, if I want to leave DD with DH in the room at night and go to the shop or lobby, it is inside the same building.
2. Poly. Rooms are big. Resort area is beautiful. You are on the monorail resort line, but also a short boat ride from MK. We sometimes chose the boat just because it was a nice ride. You are within walking distance of the TTC (travel and transporation center) which means you can walk over and take the express monorail to EPCOT or MK. This is the biggest benefit of the Poly over the other two for us. It has always been a big timesaver. We spend the most time at those 2 parks, so the easy access to either one was great. We LOVED the access to the TTC. The buses to the other 2 parks are fine- we have never had any major issues. We usually took them from the Poly, but you can also walk to the TTC. The resort grounds are very lush and green, but if I wanted to leave DD with DH at night and go to the lobby shops, it could be a far walk and not always the best lit and not open so you can see everything around you because of all the greenery. Sometimes I would get a little anxious as I would be the only person on a path with tall greenery on both sides, which gave me a silly fear of someone popping out from behind the greenery. That would be my only downside. Trader Sams has been added since our last stay, so I would bet there is a lot more lighting now- and also I'm sure the paths have more people up and down them in the evenings.
3. GF. Again, the resort is very pretty. The rooms are larger than WL and a good size. You are on the monorail line, but also a nice short boat ride to MK. The lobby has great live music at night alternating between a piano player and band. If you have little girls and are looking for a character meal, 1900 Park Fare has a Cinderella Dinner (which my DD has always loved) and a breakfast that has characters like Alice and Mary Poppins. We've never done the breakfast- too big a hurry to get to the parks- but have done the dinner many times. Although most rooms are in out buildings- the area is wide open and well lit without tall greenery on the paths, so if I wanted to leave DH and DD in the room and go to the lobby/shop area I never felt the remote bit anxious about being alone. You can see everything around you as you are walking. The only downside for us at GF is the bus service to the other parks. It often leaves a lot to be desired. We have had very long waits and due to shared buses, have had times when a bus came by, opened its doors and said it was full, but the next one would be along "soon".
We never do the dining plan. We have done the math and price wise, it would not save our family any money. Some people it will save money- it depends on how much you eat; what your eat; and your meal patterns. We have only done club level at YC. I will say it is hard to go back after you have done club level once. Whether the price is worth it depends on if you are going to use it. For us-- we don't do full pre-park opening breakfasts. DD is not a morning person so setting her there by rope drop is hard enough without trying to do a table service meal earlier. Club level was great to pop in every morning on the way to the park and grab breakfast. It was also nice to have drinks and snacks available if we were back at the park. YC with us being walking distance from EPCOT and DHS it was easy to pop in if we here hopping parks- some places we don't ever go back to the resort during the day- so it would not be quite as convenient.
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