A lot is going to depend on the costs of each of the players involved, and any sort of keeper restrictions there may be.
On the face of it, it is hard to judge. Johnson is someone I really like and will hopefully bounce back from surgery and return to being a dominant starter. Most recent reports is that he is on track. Feliz is moving from the pen to the rotation, which is a good move in the long run. For the upcoming season though, he will probably be on an IP limit, which may cap his value.