Based on the terrain that should be available.
If I would be on the South Shore of Montreal, I would definitely go to Jay. In the city, MSS or Jay would be a toss up. North shore, it would be MSS.
That being said, my Edelweiss (owned by MSSI) allowed me to ski free at MSS when Edelweiss is closed. I did it only 2-3 times in the last few years, so it should tell you something about my preference (but I'm not your average skier). It also depends of the time I have. Ottawa is also an extra 2 hours from Montreal.
I would be able to make MSS in 2:15hours and ski free on 2 runs for 210 meters. Jay and Jet is maybe double in size, but also 3:45 away and not free not me.
Regardless, I'm planning to ski in May, lift or no lift.