I own both 638 & 642, bought the 638 first because I thought the ability to fire single action may come in handy although after shooting it for a couple of years I rarely ever shoot it single action. I did some stoning on the action and did a lot of dry firing and the double action is now almost as good as single action. Bought the 642 just because it looked good and had a 2 1/2" barrel with a pinned front sight. Both revolvers shoot very well and can use the same holster. I think either one would be a good choice!