Honestly, none that keep me coming back like HN. There are definitely some decent communities within reddit if you are willing to wade through all the garbage that Reddit throws at you by default. I'm sure you are probably aware but pretty much every specific interest you might have, probably has a r/ and generally the more specific, the less trolling and the more focused the conversation.
Yea.. 4 years ago Reddit was much more like HN in this regard. It is a shame how bad it has become
HN includes a much more limited crowd. I would theorize Reddit is a more realistic reflection of our society (not that we want to focus on that, so I'm not saying it's any better, quite the opposite).
True, Reddit has been hit-or-miss. I know they tried to make Imzy, but that didn't really take (and is now closed down).