I’m going with Sanders vs Carson.
Both candidates hold the quality of novelty in terms of nation-wide. This is important in a nation that is steeped in the importance of novelty.
Sanders: Bernie brings qualities of sincerity, passion, and what I’ll call visionary pragmatism to the race. The idea of a one payer health system may seem radical, even socialist, yet he can point at many socialist health systems as costing less while yielding better results; the libertarian argument, with which I have a certain sympathy, that the context differs in that we have to support drug development while other nations simply leach off the United States, will have little impact since the libertarians, by and large, have chosen to throw their lot in with the GOP rather than the Democrats. The progressive wing (which differentiates from the socialist wing, who may be ambivalent about Sanders) will like him not only for his progressive policies, but also, perhaps against their own will, for his feistiness, i.e., for example, his gun policies.
This is no knock on Hillary – exceedingly bright, hard-working by all reports, major credentials. She’d probably make a fine President. But she’s too familiar, even when her husband steps up and hits a home run of a speech, as he does from time to time.
Carson: Regardless of the wishes of the GOP leadership (as we’ve seen with the Trump takeover of the race), Carson has perhaps the best shot at winning the GOP nomination. In this case, it’s due to the reactivity of the GOP’s membership to various charges: he’s black, he’s exceedingly well-educated and has a fantastic standing in the community as an eminent retired surgeon, and yet he’s apparently religious to a fault. Trump, to give him his due, has his business successes (and failures, although they are hardly mentioned), he has a charisma to him, and the willingness to trumpet lies and half-lies that appeal to the biases of the base; Fiorina may appear to be made of steel, but as the national press has pointed out, her grip on the issues is more than a little faulty, and her most important project, leading H-P, was a disaster. Carson has non-political credentials, which appears to be important to the GOP base, and will bring a new, yet familiar viewpoint to the office; I could easily see a replay of the important Bush II campaign moment when some voter, during an interview, declared she felt Bush had been picked by God to be President. (Evidently God hated us during that campaign. Or hated Bush.) Carson’s breezy confidence is deeply appealing, and his credentials validate many of the biases of the base.
And, yeah, this is a knock on the GOP candidates and base. There’s a difference between the trumpeted “deep, talented field” of the GOP, and it’s true nature: a bunch of power-hungry politicians who are either as goofy as the GOP base and/or leadership, or are willing to lie through their teeth for power.