Have to go with what works best for you. I shoot split--when I was starting, it never even occurred to me to shoot 3-under. Like BC said, gapping is easier from about 30 yds and in with 3-under, because the gap will be less. I did learn to gap shooting split (didn't know that was what it's called at the time, just did it). I don't conciously gap now, except on really long shots.

I like a medium/low wrist grip--feels more natural and stable for me. I don't do well with an extreme high or low wrist.

Some grips can be modified after the bow isbuilt, but some can't. Some riser designs will only allow for a certain type grip--most really short bows, like the Kodiak Magnum, have a very deflexed riser and will be high-wrist only. A low wrist can be built out if needed, with some sort of wrap.

Chad