It may help to note that the short action, or short-throw hammer, came onto the N-frame scene with the Model of 1950 changes. The short-throw .38/44 ODs became known as the Model 23 after the model designation was established in 1957, and the 1950-1957 guns can be referred to a Pre-23s. So there are three periods to distinguish: prewar (1931-1940); postwar 1946-1950, and postwar 1950 onwards.
The long action is found in prewar and transitional models. The difference is that in the short action the hammer stud is slightly relocated in the frame, and parts reconfigured, to permit a faster lock time.
The adjustable sights on postwar revolvers (both postwar and transitional) are the larger micrometer click sights. Prewar ODs have smaller rear sight assemblies.
The safety block on postwar revolvers is "safer" in the sense that it cannot fail in the way the prewar safety block did -- by getting fouled and gunked up in its channel in the sideplate so that it sticks in place and doesn't slide back into the path of hammer travel when the gun's action is relaxed. But the postwar safety block is to my mind no safer than the prewar design in a clean and properly maintained revolver.
Pros and cons will be evaluated differently by different people. Like other posters, I love the fit and finish of prewar guns. But I tend to like the transitional models because the mix of long action (my preference) with the ribbed barrel and larger sights really seems to help my accuracy when I take these guns to the range. If my eyes were better, I would probably find myself more supportive of the 1930s guns.
But they are all fine revolvers.
Just for comparison, here are ODs from 1938, 1946 and 1956: The prewar specimen has a humpback hammer, but it originally shipped with a standard hammer whose spur looked like the one the transitional OD. The transitional OD has been fitted with a King reflector front sight in place of the standard patridge blade. And all three guns are wearing non-original stocks, so don't look at the wood.
The prewar gun has the standard deep blue (almost black) high-polish finish of the 1930s. The transitional OD has the early postwar satin finish. The Pre-23 has the high-polish finish of the mid 1950s, which I think was the standard finish by then. In the early 1950s you had your choice between satin and high polish.
