It might be useful to mention that people shouldn't scroll down before doing the blind test. I almost scrolled down just to see what comments people had made about the idea of this test, but realized people might have listed their answers. Either that, or we need a spoiler function to block out the answers until scrolled over.
I kind of had the same feel as others. I tried to tell the difference by listening to the vocals, but couldn't. I'm surprised at how difficult it is to explain the difference, but the instrumental sections just sounded fuller on B. I favored B from the first listen, but couldn't figure out why. The following few listens I felt like the cymbals and drums in particular just had more range. After a few times listening, it just slowly started to sound the same or something sounded randomly weird, so I think I just listened too many times and started imagining differences. The vocals always sounded the same to me.
It would be neat if there was an automated process for creating test files like this using your own music without being aware of which file is which. Of course, you would need an answer key of some sort so you could find the solution once you've done the blind test. I feel like it took an effort to know the song and identify differences. I think it would have been easier to tell the difference if it was a song I was really familiar with.