For purposes of this thread, I think it's safe to say St. Viateur and Fairmount are locked in more or less eternal battle for the top spot, with St. Viateur apparently being the people's choice (as witness expansion of the chain) and Fairmount, while still making a great bagel (arguably, but by no means definitely, the best in town), doing silly things like tainting its dough with cinnamon and raisins and trying to pass off the result as a Montreal bagel.
Anyway, there isn't always a Fairmount or St. Viateur in easy reach (I don't count the plastic-bagged specimens seen in many grocery stores), and contrary to popular belief there are other bakeries making bona fide Montreal bagels.
So who wins the battle for third?
I've only tried two of them recently, and of those Beaubien easily takes the crown. Yes, they have some chutzpah to post a sign in the window claiming to be THE best in town, but you don't expect them to say "We're a solid third!", do you? All things considered, they make a very respectable bagel, more in the St-Viateur than Fairmount style. I buy them regularly.
The other entry I've tried is D.A.D.'s, on Sherbrooke in NDG. Sorry, Dad, your decent Indian takeout and open-all-night convenience don't excuse your bagels. To be fair, the bagels are passable when very fresh, but they have an even shorter shelf life than the good ones and are not made around the clock, so not easy to get oven-fresh. If you're in the hood, make the detour to the St-Viateur outlet on Monkland, unless you're in the mood for saag or dal.
And the other contenders are....?