I have both. The N frame #28 is a little bigger overall, including the grip. It should handle a steady diet of full power loads if that's your thing.
The K frame #19 can shoot loose, after many many full power loads. Most folks have to work pretty hard to make this happen, and when it does, usually a new hand and locking bolt are all that's required to bring the gun back to spec.
The best choice in my opinion, unless weight is a prime consideration, is the L frame series (586/686). They combine the grip size of the K frame, with a slightly beefier action designed to handle a steady diet of magnum loads, as well as a full under-lug that reduces muzzle flip and felt recoil.
When I started in law enforcement, I was issued a S&W 66 (K frame). I purchased one of the first 586's to hit the market as my duty weapon, and fired tens of thousands of rounds thru it, all double action. I never felt better armed then I did with that revolver loaded with six 125 grain Remington semi-jacketed hollow points. It was a sad day for me when we switched to the Beretta 92fs.....
In the end, they are all nice revolvers, and there is no bad choice among them. It all really boils down to what strikes your fancy, and what feels best in your hand. You may be surprised how much S&W revolvers have risen in price in just the last 5 or 6 years. I remember back in the late 80's, early 90's, there were thousands of police turn ins on the market that were going for a song and a dance - But not anymore.
Larry