I have only done Whistler (twice), South Lake Tahoe (based there and did All the resorts in the area) and Mammoth and so far Mammoth is my favourite. I have never done Europe despite living in the UK, but the OT has and he prefers North America. He might give it a go again when an IC opens in Davos later this year.

The only downside of Mammoth is its fairly limited dining options.