That's a fair question. I generally decide based on what candidates say - in context. If, for example, Jeb Bush said that illegals are merely committing "an act of love" when they commit a crime to enter our country, then I would never under any circumstances support him. Similarly, if Rubio ran as a Tea Party conservative and then pushed a bill to reward criminals who enter our country illegally, then he would be dead to me.
So far, I like what both Cruz and Trump have said. Cruz is on top in my ratings because I have seen how he responded to government power. I am confident that he would do as he promises. Trump is #2, ahead of Carson, because I have confidence in his ability to run a big organization. I'm watching all three to see if they stick to positions I support on gun rights (no infringement), Amnesty (no reward for criminals), and Obamacare (no socialized medicine).
Trump supports socialized medicine.