I agree that comfort is primary. But also, once that is found consistency is important also.
Personally I use R=middle, 5=pinky, 8=pinky for major key/chord and R=index, 5=ring, 8=ring for minor keys/chords.
Personally I use R=middle, 5=pinky, 8=pinky for major key/chord and R=index, 5=ring, 8=ring for minor keys/chords.