Rubio is a little light on experience but still has an impressive resume. He is currently in his first term as a senator. He also served in the Florida House of Representatives, becoming Speaker at age 34. That gives him leadership experience sorely lacking in many other candidates. While others have spent their time garnering attention, he has dug into the nitty gritty of many issues. He can speak intelligently on the while others stick with the generalities. He has a disposition far more suited to the presidency than Trump or Cruz. He would be an attractive candidate and would bring the all-important Florida electoral votes to the GOP.
If the choice were between Cruz, Trump and Rubio, I would recommend Republicans go for Rubio. However, I believe Bush, Christie and Kasich deserve a second look.