I'm a little biased, but I do really enjoy Vail's park. Never packed, quad right to the top of the lift, and never a lift line. Even the small parks are serviced by the gondola or chair 8, which never has a line either.
Breck and Key are fun parks, but there's always a ton of people and that "brah" vibe that I despise.
But, my favorite park days of all time, were at Cascade Mountain in WI. There's nothing like a day of riding park with 10-15 friends, no matter how small the parks are.