Honestly I think Rob Portman and Tim Pawlenty are much more unlikely to be the choices. As the OP stated they come across as boring in some senses. Plus it would be smart for Romney to pick someone that is unlike him. Portman and Pawlenty seem too similar in many senses to Romney.
Someone with a unique background and with somewhat of a different culture would benefit him. I think Rubio is high on his list. Condi is a possiblity. She certainly is very smart and articulate, but her involvement with the Bush administration could pose some unwanted baggage. Still like BadGenome I would pay money to see Condi in a debate with Mr. Gaffe Machine Biden.
My money is resting on Rubio as Kasz stated. He is popular among many conservative groups and has a very good public speaking talent. Not to mention his parents immigrated from Cuba so that gives him a unique background.
Don't be surprised however if Romney chooses someone noone is thinking about. Consider someone like Susana Martinez, The Republican Governor of New Mexico. She currently has a high approval rating in her state. She apparently has a lot of "spunk" as some would say and has many political stances that would be popular with conservatives. The only problem is she has expressed that she has no interest in being VP.
