I would choose between the BWI, the Polynesian, and the AKL.
The BWI seems to have the least number of kids, especially if you can swing concierge. The close location to Epcot lends itself to leisurely walks in and out of the park, and having close to a dozen upscale restaurants within a few minutes walk is wonderful. The atmosphere is quiet and casually elegant, and a trip to the Bellevue Room is a must during your stay.
The Polynesian just seems to lend itself to romance, with the hammocks on the beach and the lush tropical setting. Although IMHO the dining options there aren't romantic, it's a quick stroll or monorail ride to the GF and CR where there are several incredible dining options. Getting a lagoon view room generally gives a view of Cinderellas castle, which gently changes colors throughout the night.
And the AKL is the ultimate in exotic luxury. Again, I highly recommend the concierge level if it can fit into the budget. There are two tours especially created for CL guests at the AKL, and they would be memorable experiences. The Sunset Safari is limited to guests age 16 and up, so might be more suited to a romantic experience for you.
Ask away if you have any other questions, and let us know what you decide!
Anne