The Dullus Suites is swank. The staff has always been top notch. The IAD FS is one of the sorriest hotels in the Marriott chain. Lounge access isn't worth it, especially when you may have to walk a mile to get from your room to the cruddy, cruddy lounge. Anything you ask for from the hotel staff seems to be an imposition. It always seems like the guests are an interruption for them. The Suites is a no-brainer.

With that said, I would actually choose the RI Arlington Rosslyn. While many of us avoid RIs because of the reduced points, you're using a cert, so that won't matter. The hotel is quite decent. I've stayed there and would stay there again. It's a very slight distance from DCA, but enough of a distance that you won't hear much airport noise. The Metro station is practically in the hotel, so you have easy access to anywhere in the District and all the tourist attractions DC has to offer.