We are just back from Costa Rica yesterday!

CR would be a great choice. It will be a bit more of a chore to get there. Punta Islita, Los Suenos, and the JW are all a bit of a drive from the airport. I think Los Suenos about 1 hour. JW 90 mins-2 hours. Punta Islita 3 hours. Thats after a connection. The resorts are really great though.

Doesn't United have a daily non-stop to Aruba from Dulles?