The best tailor in DC is Field English Tailor. He was trained at Gieves and Hawkes on Saville Row. His father was English and Row trained.
Very traditional English tailoring - neither built up nor natural shoulders, strong chest, nipped waist. Expensive, but they are true bespoke suits - probably twice the price of a MTM BB suit by Martin Greenfield. Northern Georgetown.
For MTM, I would go with Samuelsohn. There should be a few places in the area that measure for them. One is in Bethesda. Forget the name of the shop.
- don't got to suit supply unless you want a glued construction. better off with altered off the rack from Hickey Freeman or BB. At least the suit will be fully canvassed and made from high quality fabrics.