Prof gave a good answer on foreign policy - though I'm no fan of Kasich's either. On the other hand, Trump and Cruz sometimes say absolutely ridiculous things that seriously make me question their sanity with regards to foreign policy. I've come to the conclusion that there's nobody in the field that combines great ideas (in my opinion, of course) with good temperament.
I think Kasich has good economic ideas and valuable experience dealing with the budget and as an executive. He's probably the most moderate on social issues out of any of the GOP candidates other than Trump, who couldn't care less. Some people see him as a compromiser, but behind the scenes he apparently can be a bit of a stubborn mule and even a maverick at times - a mix like that is fine with me. Better than an uncompromising ideologue like Obama or Cruz. Most importantly, he seems sane.
So basically he wins by default, by being the least worst option. I don't think Rubio is ready and he just doesn't have a record of major success as a legislator. It doesn't really help that he backed away from the signature legislation that would have helped give him that sort of credibility. The immigration issue is tearing apart the party.