I've only skied at Seymour and Cypress.
For my first season I got a pass at Seymour. They still only had the slow lifts and the full seasons pass was cheap. That was a great deal and a perfect mountain for learning to ski. There is a little bit of everything on the mountain with an emphasis on beginner and intermediate terrain. That said, you can find some trees and there are a few steep pitches such as Devil's Drop. I usually went on nights and rarely had to wait in line (except for the "Shred for the Cure" nights which I did my best to avoid.) If you went on a night or early in the morning, it was easy to find good parking (and parking is free.)
For my second season, I had outgrown the terrain at Seymour (particularly for nights.) The lift rates at Seymour also went up a little and that makes sense because they now have a high speed quad. I also planned on spending more time in the backcountry and so I didn't need a pass that would work on every weekend. As a result, I got the silver pass at Cypress which has suited my needs perfectly. Cypress is definitely a much bigger mountain and a lot of the terrain is lit at night. Lines are short in the mornings and at night.
According to wikipedia, Seymour is around 200 acres, Grouse is around 212 acres and Cypress is around 600 acres. I can't speak to the variety of terrain at Grouse.
Although I haven't skied at Grouse, it looks like a reasonable option at that price point if you want a full pass (no exclusions.) It would be particularly good if:
1) You get the Y2Play pass and start skiing right away this year and use it all of next year (only really makes sense the first time you buy the Y2Play pass.)
2) You don't want to drive up a mountain during snow and would rather take the tram to get above the snowline (although the other mountains do have buses.)