It's been more than a decade since I've published my last fanfic.
But while AO3 was a thing back then already, I stuck to only fanfiction.net. For one, I didn't want to crosspost too much. And besides, AO3 didn't seem to have the target audience for my fics. Sure, AO3 didn't have FF.net's restraints, but FF.net's restraints have never restrained me, and those who felt restrained by FF.net, I guess none of them would even be remotely interested in my fics anyway.
Then again, most of my target audience were members of one or two fandom-specific forums where I published my fics as well. And the one forum that saw all my fanfic premieres is PG-rated. I think that says something about my fics and what kinds of appeal they lack.