Originally we chose the Grand Floridian, Port Orleans French Quarter, and All Star Movies. Then Disney decided to rehab POFQ (this was back in 2003), so we switched to Caribbean Beach for our moderate.
Basically I made the decision based on location of the resorts and the discounted rates. The deluxe resorts with convention facilities tend to have better wedding discounts than those without (i.e. the GF and YC had a larger discount than the Poly or AKL). I really wanted POFQ instead of Caribbean Beach, but due to the rehab we switched.
We were surprised that our guest were really split pretty evenly between the 3 resorts, with slightly more guests staying at the moderate. To try to make the room block as accurate as possible, we went through the guest list and guessed where everyone would stay. This really worked pretty well for estimation purposes. Plus, you can typically adjust your room block later if you see that one of the resorts you choose is more popular with your guests than the others.
Also, it's a bummer that you can't choose Pop Century for your value. I wonder if Disney will change this in the future or not.