Convenient subway system. Service now extends all the way to Laval, which you can't beat.
Fast. During normal hours, trains come by quite often, unlike other cities I could name.
Clean. Once I asked a janitor (in English) how to buy a metro ticket, whereupon he directed me (in French) to a kiosk where I could buy bus tickets. At least he kept the station clean. Luckily I was able to call my lifeline for directions on how to properly buy tickets. Bonus: They weren't expensive.
Can't speak for the buses, but I love not having to drive.