The strongest reason for choosing Rubio for vice president would be based on the 1960, razor-thin election of John F. Kennedy versus Richard Nixon. Kennedy chose Lyndon Johnson not necessarily because Johnson was the closest to him in delegates at the 1960 convention, but more importantly because he could secure Texas in the November contest.
While Johnson was the "king of the U.S. Senate" in 1960, Rubio compares favorably in terms of skill sets and knowledge. Sen. Rubio has all of the acumen and ability to persuade that Johnson possessed, without the baggage and ham-fisted style of leadership for which Johnson was so well known.
As one examines the critical key swing states that will actually decide the contest this fall, it becomes clear that Romney must not only win Florida, but secure it early on in order to fight it out in states such as Ohio where the economy is improving and President Obama seems to have a chance of winning -- a win that would be fatal to the Romney campaign. By securing Florida, which most pundits believe would happen with Rubio on the ticket, Romney and Rubio could hit the road and the campaign could focus more time and effort on the other 11 critical swing states that will decide the election.
With Rubio energizing the conservative base of the Republican Party, which has grown in size in the past four years, turnout could expand for Romney. It's that extra sense of "energy" that one can feel in the air just days before an election that makes the difference between a win and a loss. While in the end Romney must win the race, he couldn't do much better than to have Marco Rubio at his side.