I'm part of the Commonwealth and I think it's obvious that the Stars and Stripes are more powerul icons than the Union Jack.
But here and now in 2013 of course it's all bout 'Murica. Things change...?
Funny, I'm American and I think the opposite. It might be because I'm used to seeing the Stars and Stripes on everything, so when I see a Union Jack I think, "that's cool."
Unfortunately the Stars and Bars have a negative connotation about them, otherwise I'd say it has a cool design as well.