Rusutsu Ski Holiday

I'm planning a ski trip to Rusutsu. I want to know how to get to Rusutsu from Sapporo and or New Chitose Airport. Is rent-a-car from Sapporo a good way to get to ? And I will go to Osaka after leaving Sapporo. What kind of transportation is the better way ? by JR or Bus ? Thanks.

It is explained here:
http://www.japan-guide.com/e/e6715.html

Is rent-a-car from Sapporo a good way to get to?

It is my personal favorite option, but beware of snow covered roads.

And I will go to Osaka after leaving Sapporo. What kind of transportation is the better way ? by JR or Bus ?

There is no bus. I recommend to fly or take the Twilight Express overnight train:
http://www.japan-guide.com/e/e5306.html?aFROM=2157_2163