Rubio isn't an attractive choice for any of the Republicans still running. He has too little experience to be a good fit for Romney, Neither Santorum nor Gingrich need him to shore up the base, and I can see Rubio wanting to be Paul's running mate.
Huntsman was probably the only one of the major candidates for whom Rubio would have warranted serious selection.
I think Romney probably has to pick someone that can energize the ticket. So in that regard, I think Rubio helps. Though I agree that his inexperience is a downside.