Mosley has the better chin of the two, is faster, more technically sound, and Vargas hasn't been the same since his back injury. I've also read that he was carrying 200 pounds not too long ago, so the weight and his conditioning may be an issue.
I'm not a great boxing capper by any means. I've only been betting for a couple of weeks, but I've long been a fan of boxing and watch a ton of it. My pick for tonight is Mosley by decision.
Also take into mind that I'm a poor college kid, so I put $2 down to win $3 on BetJamaica. I'm not putting a lot of money on anything these days.
Should be an interesting fight, though. Good luck.