So many options..... as Jim mentioned above, we don't know your budget or what you are particularly looking for, in a home base. My personal experiences relate to Hokkaido and in particular, the Otaru and Furano areas. Niseko has some amazing skiing, but it's crowded (for Japan) and very Westernized. It does get a lot of snow and there is plenty of good skiing to be had and I'm sure, decent options for studio apartments. It's just not my cup of tea, but you might like it depending on what you are looking for.
I do like Otaru, it's very Japanese and not necessarily a ski town as such, but has plenty of good resorts close by. I think if I was going to be doing a month in a ski town in Hokkaido, I would start the search in Furano. Furano is a great resort in it's own right; it has good skiing, long runs, great sidecountry, good amenities and is a nice blend of Japanese and Western culture. It's not been over-run yet! There's plenty of other resorts close by, especially if you have transportation, but there are some public transport options (though the train is not direct to a lot of places, if you have your own wheels, then you can really get around).
I think more info on what you are really looking for in your search for a location, will help people give you more focused information.
- Matt