Having tried all three, its a stark difference in how much more social Lemmy is comparatively. Its not even close. Almost all posts I've encountered on lemmy have interaction; whereas, more often than not, posts on the other two platforms have no interaction. Wonder what the driving factor is behind this difference?
It's great for seeing existing dialogue, but I think it falls short for long term discussion between more than two people.
On a non-threaded board (e.g. forums, github issues) you can watch a thread you're interested in. On Lemmy/reddit you only get notifications for direct responses to your comments.
I think some sort of option to watch/unwatch whole subtrees of comments would help a lot.