Wow - don’t know if I’ve sat down and thought about this for a long time.
Certainly thumb, pointer, and middle.
Thumb pretty much always for bass line, down beat usually on the low E and A strings, sometimes on the D and every so often on the G string if I’m wanting that extra “oomph” that only the thumb can give to emphasize a particular note or rhythmic beat.
Pointer and middle do the heavy lifting for picking duties usually carrying the melody usually on the high E, B, and G strings. I’ve found my pointer drifting down to the A every so often but that’s usually by mistake ;P. Usually if there’s a chord triad, these two and the thumb take it.
Ring finger? Melody sometimes, but usually playing a harmony note of some sort to mix with the thumb or the middle. While finger picking I tend to “pinch” chords with the ring sometimes chiming in to add a high note on the E, B, and every so slightly often the G. I find myself using the ring more while accompanying a vocalist or “vamping” in the background. I’ll use pointer, middle, and ring for position friendly chord triad positions with the thumb providing bottom end.
And the pinky - I don’t have near the dexterity to actually pick with the pinky but the little guy does come in (using the fingernail) for leading the other fingers on a downward strum (Flamenco? Perhaps?) when I need a percussive chord hit. I’ve very rarely brought the pinky into play when pinching chords because a full 5 finger “pinch” is almost non-existent for me but I’d be lying if I said I didn’t do it. From a taste standpoint that would usually be a bit too much, I think.
Wow again. Long winded response. Thanks for provoking the thought.