I'm a Finn so Moomin is, like, everywhere to the point it's still hard for me to realize it now has a "proper fandom" that isn't just Finnish shitposting
Anyway I grew up with the 1990-1992 anime myself and it's the one I know the best! I have also read some of the comic volumes as a kid but perhaps understandably I thought they were boring because all the social commentary and whatnot just flew past me. As for the books I have read some of them, but I feel like they aren't necessarily for me? I haven't really enjoyed the ones I read but it's more of a personal preference than any critique to Jansson's writing because she's honestly extremely skilled. I think it's just her philosophy that doesn't really mesh with mine all the time.
As a kid my fave was Little My but now as older I have started appreciating Sniff a lot! And I also like the anime Nibbling a lot because sailor suits and #gossip haha