Best Crab House
I will suggest Cantlers out toward Annapolis and Tim's Rivershore down near Woodbridge for out-of-town crabs where you are sitting by the water and they are cooked to order, but I think Bethesda Crab House does some good ones. Of course, there are lots of crab houses in the Baltimore area and probably worth a drive.
This question has been asked often so I will give you some links here to a few recent discussions (you may want to give the Search feature a try if you are new to the site, though new questions and responses are always good!):
This is a post of mine from two years ago when my wife and I spent the better part of a summer exploring Eastern Shore restaurants and crab houses. Actually, I've spent the better part of a lifetime doing this..
Cantler's is atmospheric; this is MORE atmospheric. Cantler's has anemic sides; this has excellent to outstanding sides.