When push comes to shove, what did they do? Did they stick with their principles or compromise? I am not sure how a debate really tests for that.
The only two that have actually done that are Rand Paul and Ted Cruz. Both have filibustered (Patriot act and Obamacare), Cruz came out on the senate floor and call McConnell a liar. Both have stood on principle and have pushed to kill bad legislation (Ex-Im bank, executive amnesty, obamacare, etc.) and worked to pass good legislation (Kate's Law, defund Planned Parenthood, repeal the CFPB, etc.)
Again, Ted Cruz has stood on principle and against the Washington Cartel as he calls it. He's pissed off the establishment more time then I can count, and has taken the R leadership to task. Smart, principled, and willing to put his money where his mouth is. He's the only candidate that I have given money to, because I truly believe that he has the intestinal fortitude to reverse the decline of America.
ANd given what I've seen of Carly Fiorina, she would be an excellent VP (the VP is supposed to be the attack dog), she's also smart, principled, and can out-Trump the Donald when it comes to going after the press.
The rest of the field would make an excellent Cabinet for a Cruz/Fiorina ticket. (Carson as Surgeon General, Christie as AG, Perry-DHS or Defense, Paul- Treasury, Jindal- State, Trump- DHS, etc.)