As it stands now I see three winning tickets.
Trump/Cruz A conservative dream ticket - GOPee nightmare ticket
Trump/Rubio A ticket that appeals to conservatives and GOPee
Cruz/Rubio A ticket that appeals to conservatives and GOPee
There are three more but they are extremely unlikely
Cruz/Trump Rubio/Trump Rubio/Cruz
The ticket that would get the most votes is Trump/Rubio IMO
Only tickets with Trump at the top will best appeal to Reagan democrats as Cruz has limited appeal for them IMO. I am unsure about Rubio’s appeal to Reagan democrats.
Trump sours on Cruz, picks a running mate from out in center or right field, not necessarily from the current Washington denizens.
The establishment would tell Rubio to pick a key state, older VP. Kasich most likely.