2 things come to my mind regarding which fingering to use in any give situation.

1. What is close and convient for reaching the note you are targeting. The easiest reach, to the new note, is usually the best move to hit the note you want to move to. So it is the path of least resistance, and the most expedience.

2. What tone do you want to sound. As you play up and down the fretboard, you will notice that the notes may be the same in pitch, but there are subtle diffrences to the tone produced. This can help to vary the way the phrase sounds. Here is a place where subtle emotion can come into you playing. This is an advanced skill, and probably not a consideration in Fundamentals 1 technique.