I wasn't sure if Uber was allowed at the Montreal Airport so I decided to try the 747 bus. Definitely worth the 10 (Canadian) dollars--clean, easy transportation from the airport (YUL) to the city center. I suppose a taxi might be a hair faster if you aren't going somewhere along the 747 route, but that comes at a price (~$45 for the fare+tip). And if I'm gonna be a good steward of the company's money without a major inconvenience, I'll take the bus.
Online it says you can pay on the bus, but I didn't have Canadian cash so I bought a ticket from the kiosk in the arrivals area (just outside customs). Walk outside and there's a line of 747 buses, get in line and they depart as they fill up. At least that's how it worked for me, arriving around 6pm. Looks like others have had to wait awhile to depart. Make sure to validate your ticket at the front of the bus as you get on--just hold it over the ticket reader until the display says tire good to go.
Read up ahead of time to find what stop you should take, the stops aren't displayed or announced on the bus.