I have never been to furano or jozankei so I cannot tell you how are the onsens there. But I have been to noboribetsu and I would think it is better you don't go since you are not booking Daiichi Takimotokan Hotel. Because if you were to go for the baths there as a day visitor (1130-2pm only), you would come back regretting not having booked to stay there.
But if you looked up the other thread I have started about onsen ranking in Japan, you would have noticed jozankei has been ranked by users in Japan as one of the top 5 onsens in east Japan. furano is nowhere on the list (not even on the bigger list which list over 42 popular onsens in east Japan).
2014 Best Onsen Ranking - www.hardwarezone.com.sg
But saying that, furano might have interesting onsens to visit. Some of my top memorable onsens are not on the list too, so it is possible to find a gem off the beaten track. I searched a bit and both the Ryounkaku and the Hakuginso onsens are interesting enough for me to want to visit.