I have frequented /r9k/ and /pol/ when I was younger(inb4 "you need to be 18 to post here"). That was more during 2016-2018. With that I fell into a really bad spot. I hated myself and as a hormonal 13 year old, hearing the notion women and jews/racial minorities cause all problems in the world obviously didn't do any good for me. I kinda started becoming a bit of an incel really. I wasn't a bad looking kid, I just had trouble making friends at the time, now it's the complete opposite. I was focused on getting a gf and losing my virginity(as many other boys were at the time) and in the height of anti-sjw culture it just made those feelings... exacerbated? It wasn't something I could share with people. Not to mention I was confused about my sexuality at the time, although I didn't really think and process it until I was 18. I obviously wasn't around for what seems to be regarded as the Chan Golden Age. I hated myself more as I kept browsing. I then quit that shit and did a real hard reset, ushering in more friends and such. Honestly it wasn't all that good. Never really enjoyed it, just got sucked into an echo chamber I found interesting. Still, it was a huge part of my formative years and it helped me with forming my own opinions on things(I am very disconnected from 4chan in my beliefs, I'm more saying that I started exploring outside of the beliefs I knew/was comfortable with and found what really works for me), so it's not something I can forget. I tend to avoid it now, except for the occasional browse of /k/ and /fit/.
In terms of my thoughts about it, the site has just always been shit, but at least it was starting as good shit. I think anti-sjw culture really contributed to it's downfall(not that it had much further to fall, so really it was more of a trip than an actual plunge). The only good thing that has come out of it was the resurgence of Panchiko. The two things I find a bit uncomfortable for now are the more frequent pedo posting on the site(not sure what this will turn into but because 4chins is touching it I'm already insanely uneasy) and the memes/jargon seeping into pop culture. From my understanding, their jargon and pop culture was really separated and now it's coming closer together. Not sure how that will turn out. I think that maybe an internet culture reset will happen in the coming years in that non-popular forums and social medias will be associated with the basement dweller types again and we go back to how things were seen in 2016. Then again, I do firmly believe tinfoil hats are a bold fashion statement. Or perhaps things will be fine and 4chan will find new terms to pull out of their ass to feel different. Who knows.
In terms of other chans, I have only been on 8chan once and that's really it. I can't stand the shit that chans do. I like this forum way better because it feels like I'm actually conversing with well adjusted adults rather than teenage boys who think saying the n-word in public is funny and owns the libs. 8chan is really boring and has too much of a sticky feel to it. New boards every day, no one can agree on what to post so they nuke the board and make a new one. I never really cared much to find more outside of those two. I absolutely agree that 4chan really just degraded in quality with those racebaiting and porn posters, no matter what board it's always a thread with a bunch of horny dudes saying they want to "race mix" and other dudes who are mad about it. Everyone is mad about everything and it's just boring to read the same thing over and over again. It's just pointless whining and jerking off.