Best bagels in the city, hands-down. Any time I'm in Mile End, I try to grab a dozen sesame to bring home. A fresh-out-of-the-woodburning-stove sesame bagel is one of best things in the world. You don't even need any toppings, it just melts in your mouth.
The blueberry, cinnamon raisin, and chocolate chip bagels are all on-point as well.
Fairmounts' bagels are larger and fluffier than St. Viateur's, and in my opinion, way tastier (they get a smokiness that St. V doesn't have). So Fairmount is where my allegiance will always lie.
Also, please ignore the negative reviews from tourists who seem to be critiquing Montreal-style bagels instead of Fairmount itself. A lot of them clearly didn't know what to expect, or foolishly compare them to NY-style bagels (they're so different). So take what they say with a grain of salt, and try it yourself.