This chart is made from a new Gallup Poll (done between July 7th and 10th of a random national sample of Republicans). It shows the net favorable ratings of the individual candidates (arrived at by subtracting the unfavorable rating from the favorable rating). Frankly, I think this shows just how much trouble the Republicans are in.
Note that the most popular four candidates (the only candidates to have over a 40 net favorable rating) are all extremists of different stripes -- Huckabee (a fundamentalist who would love to turn this country into a christian theocracy), Paul (a libertarian who doesn't believe government has a role in helping Americans or ensuring equality), Perry (who never saw a teabagger idea he didn't like), and Ryan (who thinks the solution to all problems is to cut government programs and give more tax cuts to the rich). They would all be a disaster as president in slightly different ways, and none would compromise his extremism for the good of the country.
There is an element in the party that is frightened at the prospect of these candidates, but their option is not any better. They say they would support another run by Mitt Romney (who would happily sacrifice most Americans to benefit the 1%, Wall Street, and the corporations). The chart below is from Vox Populi Polling surveys done in South Carolina (576 GOP voters), New Hampshire (415 GOP voters), and Iowa (572 GOP voters).