Well, for starters, Rubio has actually served as a U.S. Senator and didn't start running for president within six months of taking his seat.
Not that I think Rubio is qualified, by any normal standard, but compared to the Obama standard, he is well-qualified.
Huckabee certainly has the experience, but like Rubio, he is way too soft on illegal immigration and offers neither racial (another white guy), ideological (another RINO) nor the geographical balance to bring electoral advantage to a swing state.
My personal favorite is Col. Allen West who would be a plus on all three balances plus bring much needed military experience to the ticket.
Huck is a RINO? Agree he is way too loose with the budget, but he will absolutely help shore up the social conservatives.