Going with Kasich. Walker and Rubio will come across as lightwieghts during the debates. Jeb is already crashing.
In 2011-2, Romney seemed easily the smartest Republican running and even though he won, he struggled to get more support than lightweights. The party that nominated W gave Perry a big lead until Romney attacked him from the right on immigration. Then it have Cain a big lead until the 5th or 6th woman came forward. Then Gingrich's scandals were used against him. I think Rubio and Walker being lightweight is less likely to sink them than scandals or alienating conservatives.