I think Cody is more talented, but Miles seems to have turned a bit of a corner lately and is legitimately one of the most explosive dudes at 135. I think in the first round he might be one of the few guys on the roster who can match Cody's absurd hand speed. He also hits fairly hard and -- if needed -- can drive a hard wrestling pace (at least for two rounds). Cody looked incredibly suspect with his defensive grappling against a career Flyweight, so I'm not sure I like his chances against Johns if he decides to go that route.
If Cody can keep it standing and drag the fight into deep waters he can probably outstrike Miles, but it would be competitive. That said, I'm gonna have to favor the dude with less wear & tear even if I'm not convinced of his ceiling.