New York. Hollywood would be nice, maybe, Canada?
Maybe it could START in one place, then there would be a train ride or something, and you would play out the rest of the game in that location.
You know, Hollywood would actually be nice. However.. I'd really love to see a futuristic looking city like I assume Seattle would look like (at least partially intact). Colorado.. meh. They really need a location partially surrounded by suburbs that would've been wiped out for the most part, like DC was. Like I think NY would be a complete mess.. especially if they have knocked down buildings that block the streets.. and a player would soon get lost and angry (its happened to me before <_< )
I really don't know much about the layout of Seattle. But it sounds right to me.. woop woop. Boston would be interesting though. Perhaps some sea travel still exists in post-apocalyptica, eh?
Also.. I think there should be storms. http://www.myconfinedspace.com/watermark.php?src=http://forums.bethsoft.com/index.php?/topic/947221-where-should-fallout-4-take-place/wp-content/uploads/2006/04/pa27.jpg