Gamers Corps in Old Ellicott City is where I go. Unless there's something going on that night, they usually have tables open, the staff are friendly and helpful, and they're open reasonably late on Friday and Saturday nights. Plus, you're surrounded by lots of great food choices for lunch or dinner beforehand.

Only downside is be prepared to haul your games with you, as the nearest parking lots are a good 800-900 feet away, either up or downhill (and you'll be hiking uphill either way, either to start or when you finish).