Dan Toelke has popularized a two finger grip with the middle and ring finger under the nock, and no pressure on the index finger. I think some people use the index finger to help draw the bow and then take it off the string at full draw. Anyway, there have been several favorable reports on here from those who use it, and no unfavorable reports that I know of.
However, the method USA Archery advocates is to put most of the pressure on the middle finger, next most on the index finger, and the least amount of pressure on the ring finger whether drawing split finger or three under.