They're all the same thing to me, although I'd call it a couch - but up here what you call it is very tied to both the region and class that you're (or your people are) from. As we've become more mobile as a society, the class thing is less of an obvious signifier (I suspect the very VERY posh would judge, because they all go to the same boarding schools, but for the more normal amongst us, not so much).