Unfortunately, both R and L parties believe that their way is best and mean to impose these values on everyone else. It's all good until the other guy wins and you're on the receiving end of the imposition.
A constitutionalist goes out of his or her way to avoid instilling personal preference into things. The first question they ask themselves when an issue arises, is "what does our country's founding document say about this?" If still unclear in the answer, the next question would probably be something similar to "what would our founding fathers have done in this situation?" The final check is whether or not the answer errs on the side of liberty.
I consider myself a constitutionalist, however I am not a politician. My personal beliefs/preferences do not effect my interpretation of the constitution.
Ted Cruz is the best choice I the remaining field in my opinion, but he falls short of the constitutionalist that I would like to see. No one seems to come as close as he does to the constitutionalist ideal, so he'll get my vote.