First of all let me say that I do not think you can go wrong with any of them. So it's really just a matter of personal preference.
There are minor transportation pluses (like CR's walk to the MK, or Poly's walk to the monorail to Epcot, which I prefer, GF being one stop off the monorail, etc.).
We've stayed at both the Poly and the GF several times. The look of the CR (and lack of gardens to walk through) just hasn't appealed to my family.
They all have nice restaurants (plus it's easy to get from one to another).
I suggest you look at the photo threads (or the first few posts on each resort thread) to see which decor/theming appeals to you the most. The 3 are VERY different so hopefully one will appeal to you more than the others. Lots of people here have a definite favorite, but it really matters more what you are looking for...
CR has the tall building, modern decor, monorail going through it.
Poly has lush gardens, a pool at the beach, hammocks, and a tropical theme.
GF has more formal gardens, nice pools, and a more elegant Victorian theme.
Hope this helps!
