Really the best one to nominate--as in most electable, and for conservatives, most truly conservative--would be either Palin or Huckabee. Palin has the media exposure, she has the name recognition (almost everyone knows who she is, despite what they think of her). Romney might be the most electable, but for conservatives as evidenced by this thread he'd probably be a dissapointment. Huckabee might good be a good choice but his record on crime--which I recognize is important to conservatives--is spotty.
Paul is probably the best bet economically for conservatives but he's derided as a kook and has a defense strategy that neither Democrats or Republicans really endorse, and ideas on how to fight the war on terrorism (considering 9/11 to be an act of ''air piracy.'') is a bit ridiculous.
A candidate who was conservative economically, libertarian socially, and hawkish on foreign defense would be perfect.