I'm not sure if there is one "best" park...from what I skiied last season, which included Whistler and Mammoth I really enjoyed Bear Mountain California the most.
Keystone had two of the smoothest hits I've ever hit last year. That said, I only hit CO parks last year (tend to travel for steeps). Breck always has oodles of stuff,
Un my opinion though depending on what ur looking for alot of those places flip flop just depends on when u catch them how the weather is. Like I frequent PC and its been great and its been so so!!