I have both the 638 and the 442, both are great little revolvers. I've also seen some posts about the grey finish flaking off the 638, its never been an issue with mine.
I always loved the look of the shrouded Model 638. I bought one about six years ago. It isn't very accurate at more than 7 yards (at least for me that is) but again it is not a target gun and more of an up close and personal SD handgun. I've got some Karl Nill grips on it which allows me to have a better grip on the gun.
I have the 438 and the Ruger LCR. Love them both. The Smith has a better overall build quality. The 438 is slightly heavier. The Ruger has a better recoil absorption. The biggest difference is when carried the Ruger LCR rattles. The Smith doesn't.