The M-28 is an excellent gun, although I prefer the brighter finish of Model 27.

However, N--frame .357's have a few problems. If you shoot a lot, the cylinder timing will wear faster than on the lighter Models like M-19 or 586 and their stainless peers. That's because the hand has to shove around that big,heavy cylinder, originally meant to be bored for .44 cartridges. Bored for smaller .38 or .357 ammo, there's a lot of metal there! That adds strength, but also weight.

You may also experience cylinder endshake sooner on the S&W than with the Ruger, which has a unique front cylinder lock on the frame.

With truly heavy use, normally encountered only by people who shoot a LOT, like SEALS or combat action shooters, both the GP-100 and the M-28 will eventually need repairs. I'm tired of Internet posts proclaiming that Rugers are built like tanks. That's trite now, too often said. Even tanks can be knocked out. Frequently firing very heavy loads with lighter bullets will erode the forcing cone of either gun until it looks like a "tank" has encountered an A-10 attack plane. I've seen pics of a GP that was a real mess there. I'm on one Ruger board and sometimes read the other, and you see photos there that you don't on this S&W board.

I've owned several M-27's and M-28's and liked them. All of mine had either six or 6.5 inch barrels, the best for that heavy frame and cylinder, I think, and giving higher velocity than shorter .357's. I also own a stainless GP-100 with four-inch barrel. The heavy barrel lug makes a longer GP or a M-686 too unwieldy for my tastes.

Overall, in a gun needed for long - term use with a minimum of repairs, I'd choose the GP. But I'd respect the laws of physics and realize that NO .357 revolver can be shot forever with heavy loads and not need attention. Also, the GP is available in stainless steel, a real boon for a gun actually carried outdoors n all sorts of weather. The M-28 is only in a dull blue finish and is discontinued. You may have some difficulty in getting factory repairs. Ruger's repair time is usually much shorter than S&W's.

How the guns feel in your hand can be changed with replacement grips. My GP-100 wears Pachmayr Grippers and feels great in my hand. It is very accurate and comfortable to shoot.

If one of the guns in the OP has seen less use and is in better condition, that may be the one to buy. Also, I don't recall barrel length being mentioned. Keep in mind that if the Ruger is stainless, small scuffs are easy to polish out.

Finally, unless you shoot a heck of a lot, trying out various handloads, you should not be firing a lot of .357 ammo. Bill Jordan told me that most people fire Magnum ammo maybe 10-15% of the time, and he had that in mind when asking S&W to make the Combat Magnum/M-19. The .357 is not a target or recreational round. It is meant for KILLING. How many coyotes, deer, or people do you kill in an average year? Snakes? They don't need .357 power, but you'd have .357's loaded in cougar or bear country, and still not fire a lot of them at snakes.