its not terribly important,how you attack with your fingers is more important,plus bellows attack.
Louis Killen,only uses two fingers,on a lot of his song accompaniments,but he sounds good to me,
personally I find three more flexible than two,and I find the disadvantage with four comes when trying to play standing up,and trying to use the doppler effect.
but then various people have come up with adaptations which they say helps to facilitate easier playing with 4 fingers and other things.