Wattpad's community is horribly toxic. I started posting online through the website when I was in high school (2012) and it was great, but over the years its been taken over by the worst side of social media, and I've seen some really disgusting things. It's also increasingly hard to build an audience there as a newcomer (I built up maybe 3k followers in 3 years when I started a new account to get away from a creepy reader who was crossing so many boundaries, as compared to 11k on Tapas in the same amount of time).
It probably has a wide variety of stories, but has also been very much swallowed by good girl/bad boy and borderline (at best) abusive relationships because I guess that's the 'in' thing.
AO3 is pretty good, lots of friendlies, you just have to be careful because some fandoms can get pretty aggressive over certain things (not nearly as bad as Tumblr).
Tapas is hands down the best. I haven't had a single negative experience with readers or other creators, and followers here are super interactive, understanding, and sweet. I feel like I've made an actual connection with some of my readers. Tapas also supports indie writers a lot more than any other site I've come across, and there are lots of reasons why this has become my home for posting writing online.
I've also seen a pretty good variety of novels, and less focus on the novel side on the gross side of glorified abusive relationships (though some of the premium comics- especially BL- have been tending that way, which is a shame)