At this point you need to use your instincts. National polls mean nothing. Carter was ahead of Reagan by 30 points at this point in his election cycle. The national polls move drastically. They really are meaningless. Now the polls showing and election a few days out tend to be pretty good.
And by the end of April 30, of 1980, Carter Vs Reagan: Dead Heat
Polls are a measurement. You use them as data, like you would use any other information. They might not be accurate, but they are a better basis for objective analysis than what people "feel", or their "instincts" -- there are experts who HAVE good instincts, but I wouldn't trust the typical voter's "instincts", given that the polls are hardly trustworthy and they are reflective of a larger sampling of voter's "instincts" than the anecdotes we get here.
If one is arguing that Santorum can't be elected because the electorate is turned off by his views, but polls are consistantly showing he is within striking distance, that certainly suggests that people are wrong about the impact of his views on the electorate.
And if people say Gingrich will crush Obama because he can attract voters, but polls consistantly show he's losing by double-digits, that suggests that, at this moment, Gingrich isn't doing a good job of attracting voters.
Maybe Gingrich will figure out how to get people to like him. Maybe people will get more educated about Santorum and reject him.
But use your instincts -- which candidate do people know more positive things about, Santorum or Gingrich? Gingrich was in the news for decades, and among republicans had a lot of positive news cycles until he started doing un-conservative things. Gingrich has had much more money to spend this cycle putting out positive advertisement. Santorum has had millions spent telling people negative things about him, and has had little money to spend to put out a positive message.
And since Santorum isn't know, it is more likely his numbers could swing, positive or negative, but he is very positive right now in favorability.
Gingrich is very well-known, and it is likely nothing he can do can swing his favorability much one way or another, and right now it's rather unfavorable.
So my instincts tell me there is more upside potential to Santorum than Gingrich, and that Gingrich isn't performing well in his current state, and has little chance to CHANGE that perception.