When some of my friends come to Boston, I bring them to Daddy's Roast Beef (Kingston St near Downtown Crossing) for a super beef sandwich on an onion roll. I explained to them that like the cheesesteak in Philadelphia, Boston has the roast beef sandwich (without really knowing if this were for sure).
I can't say I've tried too many Boston-area roast beef sandwiches, but this one topped the current Buzzy's, Liberty Bell, as well as a chain I went to in Woburn.
I'm sure there is no shortage of roast beef sandwich places in the Boston area. Has anyone systematically tasted them for the best? Bonus points for those that have very dated decor.