Both the Niseko and the Hakuba areas are two of the best, most well-known spots in the country for foreign ski tourists.
Niseko, aka "the coldest place in Australia," is more or less completely dominated by foreign tourists. Don't expect to have an authentic Japan experience here, although you can expect some great skiing for sure. Hakuba also receives large numbers of tourists, but has the benefit that they're more spread out around the valley.
My compare & contrast in a nutshell: Hakuba offers steeper, more consequential terrain, while the Niseko area is generally more in the "fun-pow" category of low-angle, low-worries pow riding. If you're into steeps, that's plus-one for Hakuba. Niseko (and Hokkaido in general) is usually more snow-secure than resorts on Honshu (the main island), although recent winters have been bucking that trend.
After visiting both areas several times, I would have to say I prefer Hakuba and the greater Nagano area. Here's why: more resorts, more diversity in terrain at the resorts, more real Japanese culture, more opportunities to get off the beaten tourist path.
Drop me a message if you have more questions for your trip planning, I'd be glad to help.
