I’ve never worked in one, but I’ve visited the following bike parks, and this is the order I would rank them for trails quality and overall fun/lifestyle/experience, whatever:
1. Whistler BC, Canada
2. Winter Park, Colorado (Trestle Bike Park)
3. Angel Fire, New Mexico
4. Keystone, CO
5. Steamboat Springs, CO
6. Highland, New Hampshire
7. Granby Ranch, CO
8. Vail (but I was there like 8 years ago)
Some others I want to visit are
NorthStar, Truckee, Northern California
Snow Summit / Big Bear, Southern California