Rubio sucks balls.
Trump/Cruz
Trump is already smoking the South, needing no help from anyone.
Cruz is no help to TRUMP’s ticket and outside of the South will hurt it.
Sharing the ticket is not a consolation prize.
TRUMP will likely need someone with foreign policy chops, international relations, ideally with a nice touch of military associations.
If the ticket for some odd reason even needs a politician, I would hope for TRUMP-Sessions, the sage of the senate with no baggage and no grudges against him. Cruz will be an appointment. AG, maybe.