Many feel that the older guns were better made, but there's some overlap. Buy the individual gun.
Some like the 3.5 inch barrels, but I feel the ideal length is six inches or 6.5 inches, where available in a particular model. (Modal 57, e.g., was never made in 6.5 inch.)
The gun balances better, has a longer sighting radius and less muzzle blast than with shorter barrels. Velocity is higher with longer barrels.
Holster maker Chic Gaylord said that the 3.5-inch M-27 was among the hardest guns to holster well, as the big frame and the weight distribution worked against getting the gun to stay in the holster and hug the body right.
He also said this of the snub K-frame guns, but members here rave when they find one. I won't buy one with less than a three-inch bbl.
What do you want: relative scarcity and collector value or a viable working firearm?