We're staying at the Poly for our week long honeymoon in August.
I think the Grand Floridian would be nice too.....but for a less expensive resort, before we chose the Poly, everyone has told me that the Caribbean Beach is great.
I have never been to any of the resorts, so I can't speak from personal experience, but I chose the Poly over the other two because it was the best IMO for a honeymoon.