Which system has the most potential, both for some minor design fixes and a huge array of modern lenses, both AF and MF? It will get even harder to keep Sony out of your bank account when the more desirable FE prime lenses start appearing.
It might be that the smaller formats are reaching a plateau, a lot of refinement and natty usability but not so much future. The a7/r is the opposite, in the 'just cranking up' phase of development. I figure file quality and good enough usability will win out in the end.