What kind of program are you looking to do? That should also have some weight on your decision, as a school like UW has some programs that are super excellent, and others that are just your run-of-the-mill programs.
As for input on the schools: both cities are fantastic. A bit heavy on the hippies and shit, but Vancouver and Seattle are great places to be. But UBC, to me, is just too detached from Vancouver, not to mention it is a sprawly campus, I considered going there, but just didn't like where it was at (but I'm considering it for grad school at the moment). With all sorts of shit considered, UW is pretty slick.
plenty has been said already so I'm not going to beat a dead horse. But I would definitely consider what major you want to pursue as a helpful indicator.