I'm sure having grown up around the Baltimore area has made me slightly impartial but I would much prefer a night of bar hopping in Baltimore to DC. Bouncing from Fells Point to Canton or Charles Village is so much easier than trying to go from Georgetown to Adams Morgan.
If you don't know where it is you need to spend a day/night in historic Ellicott City! Fun bars and restaurants in a really cool little area. The harbor area in Annapolis is also fantastic. The historic section of Frederick is nice too!
Having spent several years living in OC the draw of going there in the summer isn't there for me anymore. I actually prefer going west into the mountains around Deep Creek. Lots to do up there in summer or winter!
Also, if you're not familiar with many of them there are loads of great brew pubs and wineries within an hours drive of Baltimore. You could probably go somewhere each week without going to the same place twice in a year. Lot's of great local food and drink.