Yeah, many years ago when living in Maryland we'd drive to the New Carrollton station and get off near the White House. National Mall close by, everything you'd want to see. Easy on, easy off, saved driving in DC.I've never used NYC's subway because Manhattan is so fucking tiny there's really no point to it as a tourist, but I was really unimpressed with DC's subway system. Its expensive. The lines fucking zig zag so if you want to go, say due EAST, you have to switch lines. And the connections are inconvenient (mainly because of all the zig zagging, so you end up having to go three extra stops to make a connection than you would if the lines ran straight).
DC vs. Manhattan subway maps: