Leon Wolf, the editor-in-chief of Red State, has just endorsed Rubio, and he makes some good points in the process. Be sure to read the article by Dan McLaughlin that he links. And other arguments for Rubio could be added to the list. He does significantly better against Clinton in the polls. He helps Republicans in a state where they need more help (Florida, in contrast to Texas). Etc.
I hope Cruz does the right thing by dropping out no later than early March. I'd like to see him drop out in the last two days of February if his polling doesn't improve a lot before then. But if he's going to stay in beyond February, I hope he at least doesn't stay beyond early March. And if Cruz doesn't do the right thing, his supporters had better do it.
Since Cruz is so young and has so many positive attributes (along with some weaknesses), he has a promising future in some political contexts (as a senator or potential governor of Texas, Supreme Court justice, etc.) But he's not good as a presidential candidate. Even if he still wanted to be president, this isn't his year. He has time to run again at least twice, given how young he is. He ought to leave the 2016 race sooner rather than later. If he would do that, it would do far more good than the alternative, and it would improve his standing in the party and his political prospects over the long run.