In my opinion:
Democratic: Ron Wyden/Elizabeth Warren. It obviously unites the various branches of the Democratic Party while attracting swing voters.
Republican: Paul Ryan/Nikki Haley. This is assuming Ryan resigns the Speakership in October of 2017 and resigns his House seat. Haley's newfound ties to Trump would keep his supporters willing to vote for the ticket.
-Neither of these are the best tickets. Both Ryan and Haley are horrible general election candidates. Wyden/Warren is OK, but a tad too far-left. And it's important to have an energetic Black guy at the top of the Dem ticket to keep Black youth turnout at 2012 levels.