I don't know that I have much to say about it. It would be hard to name an aspect of vocal technique or musicianship that Beyoncé doesn't do better than Britney. Beyoncé has a naturally beautiful voice and is in near-total control of every sound that comes out of her mouth -- flawless pitch, lots of different colors and effects. She also is an excellent musician and has ideas about how to perform a given song in a way that's engaging and effective. She has what singers call good "diction," i.e. clear pronunciation of words. I wouldn't even be tempted to say any of those things about Britney.

You might enjoy reading this blog post. A classical voice teacher was given some examples of heavy metal singing to review (from the point of view of vocal technique) for a metal blog. In addition to being interesting reading, I think a lot of people appreciated the point that many of the kinds of skills needed for good singing are constant across wildly different genres.

If you wanted me to comment on something more specific, let me know.