I'm no sifu, but lemme take a crack at this while my memory is still fresh.
If you just wanna ski, Sapporo Kokusai or Kiroro would do just fine... With Kokusai being priority if you just want cheap skiing, and Kiroro if you're bringing family and want other activities to be prepared for them. And if you want ski lessons with English speaking staff, supposedly Kiroro is better. Kokusai is less tourist oriented, so while it might be cheaper, you will need a basic grasp of Japanese.
On the plus side, Kokusai is just a bus ride away from Jozankei Onsen town for a dip or a stay - with the fully natural onsen waters of Hoheikyo Onsen nearby Jozankei being of particular interest - as it's pure, unprocessed and milky rich.
Take the dedicated bus up from Sapporo station if you wanna go up to Kokusai. IINM, there's a dedicated bus connection from the Otaru side as well, but I haven't checked or tried. As for Kiroro, you'll have to Google... but IINM it's accessible from Otaru as well.
Finally, there's also Teine... A bit more touristy but easier to access. The buses up start from a JR station in between Otaru and Sapporo (I forgot the station name). Prices wise I'm not so sure, but it should be okay. The powder is better in Kokusai and Kiroro however, or so the Interwebs says.
Check out my previous post (in the spoiler) for some pics of Kokusai and Jozankei.
https://forum.lowyat.net/topic/3280981/+1700#For details... Google. Cid will get mad at me if I spoonfeed more than I already did.
Thanks a lot for the info. i never come across this Kokusai area, i think it fits me well for my visit. initially i plan separate trip to onsen (2 nights) and ski (day trip/ 1 night). Just google the price and it looks acceptable. Since this Kokusai area is accessible via Jozankei onsen. I may cancel the hassle to travel to Toyako Onsen/ Noboribetsu onsen. Thinking of these 2 places as toyako has great view while Noboribetsu i can visit to the muzeum at Shiraoi. Of cos, to maximize the usage of the JR Hokkaido pass too. haha.
One more question, is it really compulsory to rent the winter jacket/ ski wear set?