I've only used Kbin, but it seems fairly decent as a commenter aside from some federation/stability/spam issues. I really like the idea of having access to the Mastodon side of things on top of the rest of the fediverse, even though it's hit-or-miss.
Thread wise, I suppose I haven't posted enough to be statistically solid though it seems like it's dead on the Kbin side of things and federation is even worse. I've thought about posting to lemmy.world (because 1 of my threads to a kbin community just got 2 LW commenters) but haven't made new content to do so.
I probably should join another instance but I think there is a balancing act between instance popularity and desiring conversation-of/help-with my niche interests, and it seems like that is one probably isn't going to be resolved for a while.