"Best" has many definitions. For a little while I searched for the ultimate medium frame outdoor carry. I wanted a .357 K frame sized gun for light weight and I wanted extreme accuracy with .38 and .357, but emphasis on .38 for small game. I had a Security Six originally, 3" or more at 25 yards with wadcutter .38s, not good. Got a Smith M19 about that time, a little better, but around 2" ain't that good. I then traded the Security Six for a Blackhawk, very good, around an ince at 25 with .38 or .357, but it was heavy and had a 6.5" barrel. I've kept that one, though, for hunting. Accurate gun. All these guns were excellent guns for self defense, just didn't meet my .38 wadcutter accuracy level. So, I get a Rossi M971, kinda rough after owning a Smith and a Ruger, lots of tool marks, not high attention to detail, but it shot well, 2" at 25 with .38s and .357s. I traded it, though, when I found a used stainless .45 Colt Blackhawk I really wanted and don't really miss the Rossi. Then, I bought this used Taurus M66 in prime shape at a gun show for $197 and my search for the accurate .357 medium frame outdoor carry ended. This thing puts wadcutters into 1" ragged holes and might shoot tighter out of a ransom rest. AMAZING. With a good .357 load, it'll do the same. It's as well detailed as the Ruger and Smith and has a slick DA. I LOVE this thing. It might not meet your definition of the best, but is sure does fill MY needs. I've fired quite a few .38 and .357 rounds since getting it and it's holding up very well. I also found a 3" older Taurus M66 that's nearly as accurate, a gun show deal for $180, and it makes a great IWB carry, but the 4" newer gun has the transfer bar action and has a nicer DA in addition to being a little more accurate.
There are times I wish I didn't sell the 19, considering what they go for now days. And, the Ruger was a rugged gun, but it seemed to recoil/muzzle flip pretty bad and just didn't have the accuracy with .38s, though it did fine with .357s it liked.
A friend has a 686 Smith, a FINE gun, accurate, more rugged built than my old M19, but heavier to carry. I've only fired a GP100 once and it's as heavy a gun as my 6.5" Blackhawk. Not really the medium frame guns I was looking for to carry afield. The Taurus works for me much better in that roll. For a range shooter, about any good .357 is fine. Heck, I really liked that little cheap Rossi, really. Only about 30 ounces and stainless. It may not be "the best", but it'll dang sure do the job.
There are many good choices in .38s and .357s out there. You just have to satisfy YOUR needs and what YOU want. If you're a brand freak, go for that brand. Nobody has the same idea of perfection and my criteria were perhaps unique to me. Not many give a squat about fine accuracy other than maybe target shooters, but when you're trying to hit a rabbit's head at 25 yards, an accurate gun is nice to have. I carried that Rossi the most, took the most game with it. Took quite a few early morning rabbits for camp meat on hunting trips and took a Javelina with it once. It got the job done, I just really, really wanted that .45 Blackhawk and used it in the deal cause I didn't have the cash at the time. Someday, maybe I'll get another one, but I'm real happy with the Taurus. I really don't miss the Ruger, rough to shoot, not pleasant. The Smith, well, I got a good deal for it or I'd have kept it. It was a nice gun, just the money got to me at the time and I carried the Rossi for its light weight and stainless construction anyway. It was almost as accurate as the 19 and got the job done afield just as well while I didn't have to worry about the finish. I really liked the light weight of the gun, too.
What, none of you gun snobs has mentioned the Colt Python????????
Want the finest made, finest finished, most beautiful, most classic, best action BY FAR at any price, well, toss that POS Smith and Wesson in the scrap bin and go looking for a Python. Anything else is JUNK by comparison.
