You’ll see a lot of vice president selection pieces that create long lists of potential picks, most of whom make the list simply by being prominent Republicans or because other people are talking about them. However, if you want to predict who is likely to get the nod, tracking what the potential VP says or what others say about him is useless. What matters is what Mitt Romney thinks and wants.

With that as the starting point, we have seen that Romney’s political style and personal demeanor are characterized by discipline, focus, wonkishness and caution. Whatever you think of his ideology, Romney is a very smart man and surrounds himself with articulate, smart people. Advisers around the Republican front-runner have generally been with him a long time. He is not personally showy and seems to frown on bravado. He projects competence and calm. In discussions with Romney advisers and those familiar with thinking inside the camp, I can say that the watchwords remain for a VP: Do no harm.

You therefore can eliminate anyone who is lightly experienced, untested and unprepared for the glare of national attention. Forget Govs. Susana Martinez and Brian Sandoval. Even if he wanted the spot, Sen. Marco Rubio (R-Fla.) would be lower on the list than a candidate who embodies Romney’s preference for experience.

Those potential picks who still haven’t endorsed him and/or who lack a close personal relationship with him would be a stretch. Romney is unlikely, one confidante told me, to pair up with someone whom he hasn’t observed up close and with whose character and judgment he isn’t personally familiar. I highly doubt you’ll see someone like Louisiana Gov. Bobby Jindal.

As much as I would welcome a pick such as New Jersey Gov. Chris Christie for the sheer fun and excitement of it, I think he’s probably not in the top three possible picks. He has spent time with Romney and has the former governor’s respect, and he does not lack for executive experience. In the bright lights of New York and New Jersey media, he’s been scrutinized as much as any other candidate. But he is an emotional, spontaneous politician. He is no shrinking violet, nor is he a stranger to controversy. He would be a higher risk than others.

Given all that, there are, I believe, three serious contenders. Romney knows and has evident respect for each of the three. They are all experienced and very smart. Evaluating the selection under the Romney criteria, Rep. Paul Ryan (R-Wis.), Virginia Gov. Bob McDonnell and Sen. Rob Portman (R-Ohio) (who also served as U.S. trade representative and head of the Office of Management and Budget) are far and away the most likely trio to make the short list. Romney knows and has spent time with all of them. All are personally and professionally disciplined, data-driven types. There is no hint of scandal close to any of them. Ideologically all are mainstream Republicans with a reform bent. McDonnell and Ryan are especially popular with the base. While Ryan lacks executive experience, putting together an agenda and garnering near unanimity in the GOP over a number of years (and incessantly explaining it to the public) are very much akin to how a president develops and sells an agenda. In fact, in that capacity and also as head of the RNC Trust (which put him in a position to travel around the country and meet with donors), his background is very much akin to a presidential-level campaign.

None of these candidates would be considered a Hail Mary or a hiccup in Romney’s message about competent leadership. They are all comfortable and effective with the media. They could meet the central criterion for VP: Can he step into the presidency if needed?

Each has a specific asset. Ryan might generate a little more excitement. Portman might nail down Ohio. McDonnell would certainly help in Virginia.

Each has a drawback. Ryan may draw more heat from the Democrats given his role in midwifing Medicare reform. Portman served in the George W. Bush administration (which actually looks better and better every day), and McDonnell had a close brush with a calamitous issue, mandatory sonograms. These, however, are minor, non-disqualifying considerations.

Before their price goes sky-high on Intrade, you may want to “buy” one or all of the three. Based on everything I know about them and from seven years or so of carefully following Romney’s quest for the White House, I’d be extremely surprised if it were someone other than one of these three.