I shoot split finger, I tried 3 finger under a couple of times and it just doesn't feel right to me. My release has got a lot better when I learned to have more even pulling on all three fingers instead of loading up on my ring finger like I did before and I when I began to use a pull through release, I touch my shoulder with my thumb when I release now, instead of letting go of the string, which is called a static release. These two things have helped me considerably with my release. In 'Instinctive Shooting' by G. Fred Asbell, he discusses that problem with 3 finger under with the arrow getting in the way at longer ranges, it puts the arrow too high. Most 3 finger under shooters I've seen anchor with their index finger at the corner of their mouth instead of the middle finger at the corner of the mouth like a lot of guys do, me included. Also 3 finger under shooters often have a higher nocking point, a 1/2" above center, which would put the arrow even higher.
Aaron