I could not see any noticeable difference between these images (even after enlarging them) although I have shown depth of field in earlier images where the subjects were closer together.
However, I would usually focus on the subject closest to the camera. In this instance, I think that fosussing on a more distant object will lead the viewer's eye into the image.
Exercise: Fitting the frame to the subject
What have I learned?
In addition to the portrait and landscape formats, the frame is not a fixed shape or size, so it can be adapted to show the subject in its entirety or to emphasise an aspect of it.