I try to steer as many people as I know to Signal, but I don’t want to be the type of person who accepts no compromise so I also use a bunch of others. Whatsapp is the most common, as pretty much everyone here in the Netherlands uses it. I used to use Telegram, but nowadays I trust it less than Whatsapp and all my Telegram chats have moved to Signal. SMS is only there for backup and older people who don’t use other apps. And Discord is there for people who want their messages to never be read, because that app is a dumpster fire that constantly makes me miss messages.
I was just about to post the same thing. I’ve been using Linux for almost 10 years. I never really understood the folder layout anyway into this detail. My reasoning always was that /lib was more system-wide and /usr/lib was for stuff installed for me only. That never made sense though, since there is only one /usr and not one for every user. But I never really thought further, I just let it be.