I can't seem to decide whether one is better than another. Most of the time, once I decide for certain where I want the one above the nock, I will tie on one below it. I just don't like messing with moving two nock points. I shoot split, so the second one probably isn't all that necessary.
When I shot three under, I had the same issue Bladepeek just mentioned, so I figure it can't hurt to have two shooting split either.
Also, I usually hunt from a blind or a stand, so I have an arrow nocked already. So far, I haven't needed a quick follow-up shot...or rather had the opportunity for one, lol!