Thanks tobeyondthebay's blog entry, here they have already reviewed which among the Beppu hells is the best to visit.
I'm actually hesitant to visit Beppu due to its unique location as to why there are boiling ponds. It may not be enjoyable to everyone, but I'm good to visit one hell for the experience. The Beppu hot springs or hells are not actually for bathing, but are visited to view steaming various colors of bubbly mud ponds.