I've been on lobste.rs for a long time and I'm not a fan. Lobste.rs has IMO been progressively getting worse in a way that HN has not (which has, IMO, mostly stayed the same over my tenure here which is long, even longer than the time I've been on Lobsters.) tildes.net I have mixed feelings on but am much more hopeful about its outlook. They both have the same failure mode:

1. Both sites have closed membership with invites given to users. In practice this means that some users invite people but mostly a minority of users with very strong interests/beliefs end up inviting others who share the same strong interests/beliefs in order to shift the narrative. On Lobsters these are PLT enthusiasts and FOSS systems programmers, on Tildes these are leftists. All of this:

2. Makes any conversation about topics that the in-crowd is a domain expert in (on Lobsters: PLT, FOSS systems programming) good, but makes any conversation about other topics anywhere from clueless (networking) to just bad (scientific computing, machine learning). HN's breadth makes it a fantastic resource in a lot of more esoteric topics. Networking threads will have folks chiming in who authored core RFCs or who help run large ISPs. DB threads will have DB authors talking about block algorithms. Sure, political threads often draw some pretty bad quality discussion, but the top posts on most technical topics are often posted by insiders with lots of first-hand knowledge (though the moment you get more than a few posts down, that changes.)

3. Creates identity-based politics around the in-crowd. Anti-FOSS viewpoints on Lobsters are heavily criticized. Liking Go used to get you piled-on, though these days it happens a lot less frequently. Oppose software minimalism takes and get lots of pushback. Rules are fine to break if the in-crowd agrees with you but are much more brittle if the in-crowd disagrees with you. You have to have a thick skin if you want to oppose the in-crowd on Lobsters. The site is mostly driven by the whims of its posters and pushcx, which the rules are a thin veneer atop of. There's a lot of snide commentary and petty negativity on Lobsters and a lot of it is based around insulting members of other communities (insulting folks on HN is pretty much a pasttime for Lobsters.)

The big differences with Tildes and Lobsters are that Tildes is a general discussion forum and Lobsters is not. Correspondingly, Tildes's mod Deimos has a fairly light touch moderating the website, which makes me much more hopeful about its ability to build a healthy community. Lobsters' current head admin pushcx is IMO an extremely overbearing mod who bans first and asks questions later. Sometimes I think a topic's survival on that site is based purely on his mood. If pushcx doesn't like something you're posting there's a high chance it's going to get deleted.

While Lobste.rs certainly started out having a more technical focus, over time it has essentially become a longform discussion platform for folks in FOSS Mastodon circles. If something is popular in those circles it'll get upvoted and discussed on Lobste.rs, if it's unpopular it'll get booed. On HN you can discuss a much larger variety of technical topics and get reasonable answers from insiders. Just avoid the political threads and the flamewar-du-jour threads (crypto and ads right now, who knows what it'll be tomorrow) and you'll be fine.