My friend lillehafrue sent me an invite to An Archive of Our Own (aka AO3) and I accepted. (Thanks, lille!) Posted a couple of small one shots, neither of them in my primary fandom.
Since I’ve posted at eFiction sites, the interface wasn’t as daunting as it would be for those who haven’t and I have some knowledge of HTML coding, which helps. The “warnings” business was more than a little confusing. I ended up deleting my first one shot because I couldn’t figure out a way to edit the “Author chose not to use archive warnings” in favor of “No archive warnings apply” (because they didn’t). So it still has some bugs to be user-friendly. (For all it’s complexity, eFiction is easier.)
Some of the Thunderbirds writers I know are there. Most aren’t, the elites in particular. There are only a handful of Thunderbirds stories, which means that ff.net is still the biggest archive. If I use it for my Thunderbirds work, I’m going to take my time putting it all up. (Can’t import from ff.net anyway; ff.net has blocked that.) At least no one is going to be using my penname there.