AO3 vs ff.net is a bit like DW vs LJ in that the archive is newer and more customer focussed and smaller but friendlier for that, whereas ff.net doesn't have to please people because it's just so huge they know they're still popular.

Oh, I think that's an excellent point! :) And yeah, I really love their interface, as both a writer and a reader. I was awfully skeptical when the idea was first announced (I didn't see why we needed another multifandom archive when we already had ff.net and DW and LJ and all the individual fandom archives) but after the first time I used the archive, there was just no going back. :D