WE have stayed at CR, Poly, BW, and GF (recommended in that order).
I like CR because you can walk right over to MK. However, the Poly is almost neck and neck for our favorite monorail resort. I guess I am a sucker for the nostalgia that both of these resorts were the originals when MK opened.
When it comes to theming, I believe the Poly wins hands down.. I loved smelling the luau smells, the Poly inspired music piping thru-out the areas, and those tikis grew on me!
A few weeks ago, we did a split stay- several days at BW and then over for a week at CR. I love the Epcot area resorts. WE also stopped in at Yacht Club and the Beach club to see their decorations and liked those resorts too.
I think you need to consider your length of trip, your budget, and what you plan to do on your trip. If you aren't going to be at MK very much, then look into the Epcot resorts - the ability to walk over to Epcot and DHS really convinced me to stay over there more often!
But if you are more into MK and want to focus on that area, then consider the monorail resorts... and I lean towards CR because if someone starts to meltdown, the ability to walk right back to the resort is a huge plus... and I say this from experience!
Bottom line - go with your gut! If there is a resort you've been really wanting to try, do it! Then check out the different threads for each resort you may be interested in. Each and every time I have relied on the DIS threads and the lovers and fans of a specific resort are usually very helpful and kind to answer questions.