There's no real official 4chan alternative, i guess /co/'s bunker at plus4chan counts , so everyone is at a hundred different image boards. Plus reddit, facebook or wherever anons came from before they discovered 4chan.
Refugees are even using the comments section at
https://downdetector.com/status/4chan/ to shitpost at now. They're calling it /downs/ and have made over 5000 comments have been made since 4chan went down.
Personally, I've been lurking the kiwi site because they're obsessive enough to be up to date on 4chan's status and I've been looking through various other chans to see if there's an actual good alt. This one seems the most normal to me.
I think 99% of the refugees are also lurking random alts, because everywhere else feels too strange to post at. The topics or posters aren't familiar enough to evoke... communication.
I think it's weird that so many alt chans are still alive, since most of them only existed due to 4chan being so unstable for its first 7 or so years. Places like wakachan actually got big and coexisted with 4chan after 4chan became stable, but it was an alt chan still and was too big to stay alive. Smaller sites i guess managed to stick around due to finding smaller communities comfy... or stubborn owners.