I prefer Cruz on the issues, but think Rubio (whom I prefer to Trump on the issues) simply has much better shot at appealing to younger voters. Though they're basically the same age, Cruz just comes across as less relatable to young people. Rubio is the cool dad, and Cruz isn't.
Then I have to cross my fingers and hope Rubio stays with no longer supporting the Gang of Eight bill. Perhaps a misplaced hope, but given that I don't didn't think Cruz can win, it's the best bet I've got since I disagree with Trump on just too many issues to support him in the primary.
Trump’s rallies are packed with young people. Get a clue.