Kirk here with an article comparing Kurokawa's hot springs with Yufuin and Beppu. Of course, they all derive their heat from Mt. Aso.
The Ultimate Kyushu Onsen Guide: Kurokawa vs. Yufuin vs. Beppu
Kyushu’s Best Onsen Escapes: How to Reach Kurokawa, Yufuin & Beppu from Tokyo