The best way to describe a CO flight sitting in Y to and from the UK is that it's just like a domestic flight but it's a longer flight time and you get a larger meal. Same planes, same people, same safety video. VS seems a bit more "special" for the trip and the cabin crew accents adds to the novelty. I've never flown AF so I can't comment. I've found VS seats on their A346's to be more comfortable than CO's Y seats.