There are only four viable candidates.
Rubio is going to be the Establishment/moderate candidate, Cruz is the conservative candidate, Trump is Trump, Carson is the low information candidate.
Carson is slipping. His fifteen minutes are up. People are realizing that politically he’s just too shallow. Brilliant doctor, but not presidential material. Would love to have him in a cabinet post, but nothing beyond that. His foreign policy ideas are lacking to put it mildly and he’s on the wrong side of the second amendment and immigration.