I'm a registered Republican. But I'm embarrassed that Ron Paul has to be associated with the other three. I'm happy that the popularity of his ideas seems to be having some impact on them, and even Obama (or at least on their talking points). Government policies that are invasive, illogical, and cost too much (particularly more foreign entanglements during an economic crisis) are unpopular with nearly everyone.
Romney is probably the best candidate of the three. But I think he is perceived by a lot of people to be a poster boy for the economic mess we're in.
Newt has been bashed by everyone he has ever worked with...and an ex wife or two. Women in general (and many men) don't like or trust him.
Santorum is...Santorum....assuming that is Italian for insanely conservative, illogical, and inflexible.
If elections are won by carrying the white, over 40, conservative, happily employed, male vote...then Obama will lose.