I'd put in a plug for the North Bethesda Marriott. It is directly across the street from the White Flint (Red Line) metro stop. It has a very nice Concierge Lounge. The parking situation is not really clear to me. We stayed 2 nights but there was no charge for parking (I'm Plat) but I think it might vary depending on whether there is an event at the connected conference center (when I believe they charge? but again, it wasn't clear; just was happy that they didn't charge).