A:
The MIXR are really the only Beats that I was really wowed by. They are LOUD, and pump a lot of music out into your ears. I went with the QC15, however, due to the acoustic noise canceling, as well as the wonderful Bose sound. I listen to some electronic music, and they have the right amount of thump, and sound great.
Then, there's times when I just want to block out the world and not hear anything, and the QC15's are great for that, too.