I regard Newt as the best of a bad lot, he's flawed with his arrogance but he is definitely a highly-intelligent no-holds-barred fighter with a wealth of experience in how Congressional sausage gets made and how the top levels of the Federal government actually work, unlike any of the others.
I simply do not trust Romney on several key issues and regard his Conservatism as something that would last just exactly long enough to get him elected, and not a nanosecond longer. While he does stand for a sounder fiscal policy, compared to Obama, anyone would; but, he has zero exposure to foreign or military affairs and I feel he would mistakenly think of the rest of the world simply in terms of suppliers, customers, and competitors rather than realize, as Clausewitz said so eloquently, 'War is a continuation of policy by other means' and there are things at stake for which a business background is not just weak preparation, but could be actually counterproductive.
Santorum would have so much LGBT money pitted against him (Which is a lot of money, since not raising kids leaves one with a much higher-than-average disposable income), as well as all the MSM with no pretense of keeping the claws hidden, that I can't see how he could win. There would be a Gay SuperPAC that would buy all the available airtime for two months before the election to slime him, with the overt support of all the MSM bone smugglers and their butt-bbuddies. I just don't see how he could possibly overcome that.
Ron Paul has some great Libertarian ideas. His fiscal ideas are mixed (Some of are good, some not too good, some totally unpredictable in effect - and many of each with no chance of getting through Congress whatsoever, no matter which party controls it). His views on military and diplomatic matters are so primitive as to make Romney's actually seem sophisticated by comparison, which is scary on both counts.