The problem is that there is not agreement as to who that is, because conservatism isn't a monolith. In particular, you have the tension between social conservatives and libertarians. Santorum is the strongest social conservative, but is also not as much a small government guy as some of the others. Gingrich kind of pitches and yaws between small government conservativism with occasional grandiose ideas. Paul is probably the most small government of the bunch, but has weird ideas on national security and no social conservatism. And Romney, for all his flaws, may be the biggest free market proponent of the bunch (other than on health care) except for Paul, but without Paul's nutty foreign policy.
In any case, I think "conservatives", however you might define that, should get behind the person they think is the most conservative candidate who they also believe can win. Ignoring the ability to win the general election is foolish, in my opinion, unless symbolic votes are your thing.