Tough call because none are really fantastic. I would never recommend someone to come to Ontario specifically for the skiing/snowboarding. That being said, we make do with what we've got...
Blue I find over-rated and crowded, but it does clearly have the best village. If you were looking for a place to go for a full weekend of partying and riding, then Blue is the most suitable. It's also a pain in the ass to drive to.
My preference would be for either Mt. St. Louis Moonstone, or Horseshoe. They're fairly close to each other (you can see one from the summit of the other) and both much easier to get to than Blue. In terms of separating those two:
- MSLM has a better park and two pipe runs
- MSLM has more runs
- MSLM has more lifts, and faster lifts, so you're typically not waiting as long (Horseshoe is alright, but can be a wait at times)
- Horseshoe has a greater diversity of runs and faces of the hill (MSLM is pretty much come straight down and pick a fork that will still go mostly straight; Horseshoe at least winds through the woods and pitches terrain in more directions)
- Horseshoe has a better bar/restaurant and chalet facilities (Beavertails!), though MSLM seemingly has better cafeteria food
- Horseshoe has more "other" activities, like dog sledding, tubing, and cross country
As for where I ride most, I work close to Chicopee, so it's easy and cheap to go there after work when I have the itch. It's just not very much of anything beyond being cheap and close at scant over 200' tall.