US two-dollar bill 1976 which mint is the scarcest?

Huge numbers of $2 bills were printed(*) for the Bicentennial so none of them are particularly rare.

More value would be attached to one with an unusual serial number (e.g. 12345678 or 23232323) than would result from differing Federal Reserve District letters.

(*) To clear things up, the Mint only makes coins. All bills are printed by the Bureau of Engraving and Printing, which makes them for each of the 12 Federal Reserve Districts. In 1976 there was only one printing facility, in Washington DC. In 1990 a second printing plant was opened in Fort Worth. All bills are made at one of those 2 locations regardless of the district that distributes them.