Rusutsu was very nice, but smaller than many other resorts. My "kids" (30 somethings) enjoyed heading off into the trees.Oh that is just beautiful. We have a booking for Feb 2023 in Niseko, and will also go to Shiga Kogen and/or Nozawa Onsen on the same trip.
Niseko is more extensive.
Sapporo Snow Festival is 4 - 11 Feb.
We had a night there last year to check out the snow and ice sculptures - worth a visit if you can build into your itinerary.