If you do go to FFX, let us know what you think. I considered going to FFX for my oil change recently (I live and work in McLean) but decided I'd try Sterling after reading up on the various dealers. A little out of the way, though.
Sterling has a good rep and they seemed fine. I assume they'd be good for a more major service issue, but I'd probably go to Passport in that case because Passport also has a good rep and I'd be much more likely to get a loaner car there if I needed one.
Sterling gave me a call the next day to make sure everything was fine.
Also - take a look at this. Independent BMW service shops in this area, with short descriptions/reviews. I thought about going to one of them for the oil change. I'm sure these guys would be cheaper for non-warranty work:
http://www.dvsmith.net/bmw/dc_service_shops.html