There you go sounds like you have an answer also just realized mount tremblant is the only one not on a weekend so that could be nice as far as crowds go.
Mont Tremblant is cold as fuck. That being said, love the small parks tossed in around the mountain and have always had an awesome time with friends. We used to rent a chalet near the mountain each year and it was tons of fun. I know most of the times I've gone in late December/early January the big park (Adrenalin) is just opening, or not quite open. Depends partly on snow so keep in mind it may not be open.
Haven't visited Stowe or Kill so no input on those.