Rand Paul is the leader in an online poll conducted by You Choose 2016, which is connected to FreedomWorks. What's interesting is that Marco Rubio is #2 in both the favorite and least favorite categories. This could be a reaction against him being almost completely silent in the fiscal cliff battle and because some don't consider him to be a natural born citizen because of the citizenship status of his parents. Granted though this is an online poll so the results are always questionable regardless, but it's still interesting.
Here is a screenshot of the results so far: