I liked the Hyatt Regency Capital Hill the last time I stayed there. I was on business for one night, but everything was nice and it was an uneventful stay. The location is great, about 2 blocks from Union Station (Red Line Metro) and the rooms were clean. I was on the top floor in a regency room, but I can image all of the rooms are fairly nice. The club was small, but had everything I needed.
I liked it so much, I am heading back for an extended Labor Day visit using a SU. Not a bad hotel for about ~$120 a night, plus you can use the costco promo code to get a hotel credit every night of your stay. Might be helpful if you plan to eat on-site or rack up other charges.