It’s generally preferable to make scaffolds out of smaller shoots. Bill Shane has mentioned choosing shoots too large (relative to the size of the trunk) is one of the more common mistakes commercial peach growers make. He says choosing scaffolds less than 1/2 the diameter of the trunk (I prefer less than 1/3 the diameter of the trunk) will reduce the risk of the tree breaking down later on.
If the scaffold is too large, it won’t form a proper collar on the trunk and will cause the tree to split under a heavy crop load. I’ve noticed this is worse for some varieties than others.
Shane recommends commercial growers wait until the second season to choose scaffolds, so that smaller shoots can be selected. This is difficult for commercial growers because everyone wants to get their trees into production as fast as possible.