Exercise:Objects in different positions in the frame

For this exercise, the task consisted of taking series of photographs with the subject in a different position within the frame on each photograph.
The subject i chose to photograph was a person walking a dog in a field.
The first photograph i took was natural, i didn't put to much thought into it, i simply aimed at the subject and took a picture.

 The next photograph i took, i tried to get the subject within the center of the frame, although this picture is not much different from the 'natural' shot i took.

 I then took a photograph with the subject at the edge of the frame. Looking at this photograph, having the person at the edge of the frame appears to change the main subject from the dog walker to the field/trees. There is a line of green grass going from the front corner of the frame to center which draws you attention to the center of the frame as apposed to the person on the edge who somewhat looks like that have accidentally walked into the photograph.

 The final picture i took i tried to the subject in the photograph slightly off center within the frame.

My favourite photograph out of this set would be the one with the subject slightly off center. I like this photo because it seems to flow better than the others, the person is walking in the direction of the grass, towards the large green grassy area where everything in the foreground of the photograph seems to point. It is obvious in this picture that the person is the main subject in the photograph, by  its positioning near the center of the frame, unlike the photograph with the subject on the edge of the frame. the fact that the subject is slightly off center, and not dead in the center of the frame, to me, makes it look a more natural photograph.