I switched to 3 under because I didn't realize the amount of pressure I was putting on the arrow when I shot split finger.

Watching a video of me at full draw split finger, you could see that the arrow was bent.  Translates into a cleaner release.

Skinner

I just switched to three under last week.  On a whim I thought I'd try to give it a shot...

Immediately my grouping seemed more consistent, things felt better all around.  I have a low anchor, this brought the arrow up closer to my eye.  It may have improved my release too, not sure.

Considering trying 2 under as well, just to mess around.

I swithched last year.  Cleaner release, better sight picture for me anyway.  It just feels more natural to me.  Doubt I'll ever shoot split again.