I agree a lot depends on the time of year you visit disney, plus the location of your room. One time at BC we had a room that took us forever to get to (it seemed...), but once we got there we were so isolated that we heard nothing. Another time at BC, we had a room that was in a main traffic zone and therefore we heard lots of people, kids, running down hallways, etc. So, no matter which resort you choose, a lot will depend on the location of your room and also how busy the resort is.
As far as a moderate resort that has a more "tranquil" theme, I'd say POR has a great relaxing theme. The other moderate we've tried is CBR and we felt that theme was more upbeat, sort of bright and beachy, so I wouldn't personally classify that one as quiet.
As far as deluxes, we've tried most of them and I'd say AKL had a relaxing feel to it. It's somewhat isolated and does a good job of making you feel like there is nothing around it.
Some of the deluxes are geared more towards adults and therefore can seem quieter than other resorts. YC comes to mind as one of those. The lobby area is quite elegant and we don't see kids running around on a normal basis. The GF also has an elegant feel to the lobby, nice quiet music playing, etc.