This was the original question to me:
First, it would not be a primary carry gun, mostly just a plinking gun, and to help when I sometimes train new shooters. I have a Ruger Mark IV 22/45, and a Ruger SR9c. So this would be just one other gun that would fill a gap, and I think it would be right on the money for those who just want to have a gun for home defense, and in reality are not going to be a huge gun person, with the gun sitting a lot.
I am thinking about a 4" barrel, double action, .38 special, and not concerned if it is not rated for +P ammo. Mostly due to how it will be used, and also due to the extra cost.
This was my answer:
I think you should consider the used market. Look at the revolver checkout guide.
Used guns that I would recommend: S&W Models 10, 15*, 19*, 64, 66* and 67*. Ruger Security Six*, Speed Six and GP.100*. The ones with asterisks have adjustable sights, though there are some GP.100s that have fixed sights. All are six-shot.
The Rugers are pretty tough guns. You can still, with luck, find Security Sixs and Model 10s for under $400. It wasn't too long ago (four years or so) that as for the Smiths, all but the 19, 66 and 67 could be found for ~$300.
You might find one that is a little finish-challenged. I've bought two Smiths (a 1920s M&P and a Model 10) that were kind of gnarly on the outside but they were fine mechanically. They make good shooters. A lot of sem-nasty looking guns were ex-PD or security-guard guns that were carried a lot and shot very little.
You won't wear any of them out with standard-pressure .38s. If they are occaisionaly oiled and cleaned, they'll be in your family into the 22nd Century.
Another commenter suggested a gun chambered in .327 Federal. From what I have observed, it is a fantastic cartridge. Shooting .32 S&Ws or .32 Long has little recoil. But I have not seen any .32 catridges for sale that are cheaper than .38 Specials.
I didn't recommend Model 13s or 65s. Those have become very pricey of late and, in answer to the original question, they don't bring anything to the table. The only reason that I mentioned Model 19s and 66s are that they are still available.
What I don't recommend, for shooting a lot, are old Colts. On double-action Colts, the hand (the part that moves the cylinder around) is a wear part. The hand is the part that holds the cylinder against the cylinder stop (or bolt) for the famous Colt "bank vault lockup". It's designed to be replaced by a qualified Colt gunsmith, a species of critter that has become rather rare. If you look at a used Colt and the cylinder doesn't lock up tight when you have the trigger all the way back, that's a hard pass unless you know somebody who can fix it.
I don't recommend anything Taurus. Some of them are fine. Taurus has a lifetime warranty, which is nice (S&W's "lifetime warranty" applies only to the original purchaser). But if the gun needs work, it has been true that you have to pay to send the gun to the warranty center and you have to pay to send it back. Most gunsmiths won't touch them.