When I started shooting (too many years ago to admit) I shot split finger. It was the only way I knew to shoot. I drifted away from archery for a number of years. Actually, I was away from just about all hunting. My knee was so shot, walking or standing for any length of time was excruciating. It took all the fun out of it. Then I had knee replacement surgery. It was the best thing that ever happened (short of marriage and the birth of my kids). Last year I decided to get back into bow hunting. I started out shooting split, but my index finger blistered, so I tried three under. I shot well enough to take my first archery deer, but the bow seemed too loud and it just didn't feel right to me, probably because I started out shooting split. I got a different glove and went back to split. That is where I'll stay. I anchor with my middle finger at the corner of my mouth, my first knuckle of my thumb behind my jaw, and the fletching of the cock feather just tickling the end of my nose. I am confident that anything within 25 yards is in mortal danger.
As others have said, find what works best for you. My eldest son and daughter both like three under. My youngest son shoots split. I am just glad they all like traditional archery.