I love this area! Home to some of the best festivals, I come here several times a year for the Jazz Fest, Francofolies and Montreal en Lumieres. Everything is always set so nicely, there's always some sort of installation to admire like art displays or just pretty lights and water fountains you can splash in.
There's a good combo of grassy areas, stairs and cemented areas to sit or stand in. Even if there is no festival going on, hanging out at Quartier des Spectacles, is fun. There are some great restaurants nearby and you're really in the heart of downtown.
Since May 2013 they offer free public wifi, which works surprisingly well, so making those "check ins" on Yelp or Facebook to share your awesome concert becomes even easier!