Something very important to us is overall ambiance of the resort, location of the resort in relation to parks (walking path to park, monorail), and views from the resort. That puts a lot of different choices in there for us. We've loved BC for many years, mainly when our kids were babies/toddlers as the sandy bottom pool was
almost better than the parks. However, now our kids are almost teens

, and we've grown to love Poly for the reasons listed above -- the atmosphere is very tropical and relaxing, monorail, TTC, Ohana dinner, and the views at Poly are the best we've seen so far. Having said that, we've recently returned from our first stay at GF and we were blown away by how much we enjoyed it! The main building offered great shopping, the band or piano always playing beautiful music, monorail, short boat ride back from MK, great balcony and views!
We've also stayed at CR and loved the walking path to MK...also loved having Chef Mickeys right there when our kids were
really into that restaurant. Again, like BC this resort was special to us when our kids were younger. We will be staying at BWI in a couple months and suspect we will love it there as well -- we stayed there when our kids were around age 2 and thought it was just "ok," but I'm thinking now that they're a bit older we will feel differently.
We've also stayed at WL and AKL and while we think they are both architecturally gorgeous, we did not care for the room size (kind of cramped for our family of 4) or the bus service. The view at WL could've been pretty good but we had a closed panel balcony so we really couldn't enjoy it too much. AKL obviously has the nice view of animals if your family is into that. All in all, we prefer the resorts that offer walking paths to parks and/or monorail service.
So right now, Poly and GF seem to fit the bill for us as favorites. I do think your favorite may depend on the ages of your kids (if you have kids...) and what type of resort atmosphere you enjoy.