Retrocession seems like the best way to go. I'm sympathetic to proponents of DC statehood, but the way statehood goes in the US, we'd need to find a (perceived) Republican "buddy" to become a state at the same time, and that's nigh impossible. Giving the District to Maryland isn't a bad way to go, and has the nice side effect of reducing the number of jurisdictions in the area - coordinating local services (e.g., Metro) is a total nightmare. Cheers to jim and muon for pointing out ways to make the 23rd amendment less of an issue!
I agreee, consolidating jurisdictions there'd be good. Which is why DC should become part of Virginia.