We stayed at Ki Niseko and had an amazing time. They have private onsens you can reserve for free and though their spa is small, it's shockingly affordable and the massages were amazing. Their restaurant was equally high quality and very affordable for the number of courses. We usually don't eat at hotels but we were there during shoulder season so a lot of the more popular local joints were closed. Overall I thought Niseko was a bit too touristy (more Australians and Americans than Japanese!) But fun.

Houzuki Udon is a must. Beautiful location a bit outside town and they serve the best udon I've ever had.