The smaller the better. A bow is just a machine and can produce the same shot time after time. The major difference in accuracy is when somebody wraps their hand around the riser--the human factor. The less contact made with the bow makes for better accuracy.
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Martin Silver Star Shooter
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I once got a great deal on a compound bow years ago. The huge grip fit my basketball hold with one hand and the 30 pound draw wasn't wanted by many archers.
I prefer a smaller grip with fairly squared edges. I think you will find this type of grip is more accurate, and will shoot more consistently for all shooters once they learn proper technique.