Love the song. I heard "The Sound" on a local rock/alt radio station the other night at like 1AM (I'm working weird hours right now). So, I'm thinking that'll be the next US single Maybe they're saving "She's American" for the third single? I agree that it has the most appeal.
"The Sound" is definitely their current big push single, for a couple months now. They performed it on SNL and The Tonight Show around the same time the album and music video was released, and easily could become their overall most successful single.
I think it's going to be a slower build on The Sound. I think headed into this summer it will continue to gain popularity. I'm hearing it out and about a lot lately and it's getting radio play out here.