21 P or Mark & Orlando's ?
Forget 21P. It's now closed. I think it closed early last week. Looks like they didn't file their necessary permits....
I've eaten at Mark & Orlando's 3 times in the past 3 weeks. Excellent every time. The grilled caesar salad is so good. Ask the waiters what is freshest. They won't hesitate to suggest and their recommendations have been spot on each time.
There are lots of good restaurants in the Dupont Circle area. While 21 P and M and O are close, they can also walk to Firefly, Hank's Oyster Bar, Komi, Nora, or The Tabard Inn. Of the lot, I'd recommend Komi or Nora for expensive and needing a reservation, or Firefly or 21 P for a little less and easier to get into.