Rubio will be one of the last three contenders standing almost certainly. The question is though if he can beat Bush in the end, who has a much stronger war chest than him currently. I think he could, but I'd still consider Jeb the frontrunner for now, despite him not even being nearly as coherent as Rubio on foreign policy. I think there's at least a 70-75% chance that either Bush or Rubio will win the nomination in the end. Probably even higher.
But Jeb had better get his act together and soon. I have found him to be completely underwhelming on the podium and as a campaigner, and lacking in dynamism of any sort.