Squaw Valley/Alpine Meadows. Yeah, it's my home mountain, but rarely does a place truly compare...
Then again, I haven't been to Europe or Japan and i've only had sporadic days in Whistler (never a pow day), only hit up altabird and Jackson Hole 2 times each, and I've only been to Mammoth about 11 times, and 7 or so of those times were late season parklap days, once everywhere else is mostly closed.
I will say though, places like Stevens Pass and Crystal Mountain up in Wawa deserve some mad respect... same with the likes of Big Mountain and Big Sky in Montana. Bachelor is also crazy fun if it's a tuesday after it snows a bunch, and you just go Summit down to Rainbow all day long, shredding constant pow.