I highly recommend this location (Q2N) if you're renting with Avis. While it's no longer at the bottom tier in terms of prices (JT1 is cheaper by $1-2/day typically), there are always cars available and I never had to wait during check-in due to a shortage of cars in the lot. And it's still much much cheaper than the downtown Metcalfe location charging upwards of $15/day extra if you pick up there (tip: you can pick-up at this location and return at Metcalfe without incurring the $15/day fee).
The franchisor Nelly who serves the counter most of the time is easy to deal with. During busy weekends when all locations are displaying "sold-out" in Montreal, call Nelly directly and she will find you a car. I also often get free upgrades without even asking (e.g. rented compact class and got a Mini Cooper S). There was once where I realized the car only had half its tank full after driving out of the lot - I phoned the counter and Nelly put a note on the rental and I didn't need to drive back. I'm very satisfied with the service.