I instruct people that there is not a right or wrong way, just an appropriate way within the context of the song or tune. Sometimes we need the first (index) finger to fret a note behind the other fingers, like C at the first fret second string to make a Gsus4 chord, and other times we need a finger to fret the D at the third fret second string in the middle of the chord, and yet other times we need the pinky to fret an A at the fifth fret first string for a G9...etc...

Moving from chord to chord is another determining factor. Often moving from open C to open G requires one fingering, while moving from barred chords to open G (and back) requires another.

Particularly among fingerpickers, who are less concerned with playing every note of the chord than a strummer, and may be playing melodic runs throughout their chord changes, fingering should be determined by the requirements of the song. With the example of G given here,we don't always want to hear the third (B) as high as the second string and would rather have a D there, leaving the third interval on the fifth string (second fret B).

Consider the context before you settle on a fingering.

Clear as Mud, Cat?

Mooh.