I read Twitter bottom to top, because a lot of people I follow tweet evolving thoughts over the course of an hour or two, which Twitter’s conversation UI doesn’t tweak to. Reading top to bottom is super confusing. Also I like that reading oldest-to-newest gives a clear ending point—when I get to ‘now’, I’ve reached the end of Twitter and have to go do something else. I don’t regularly read Facebook or news websites, so I don’t have any developed habits there. When I do read Facebook, I find its timeline UI pretty frustrating.