Everybody has their favorite, as do I. Rather than a flat-out recommendation, I'll try to elaborate on the what and why.
The 66 is a stainless version of the 19 "Combat Magnum", one of the most popular police sidearm until the late 70's. IMO, it is the most graceful, well balanced of the Smith .357s. It was discontinued in favor of the heavier L-frame 586/686 because the K frame barrel is relieved to clear the crane, creating a thin spot in the forcing cone. This led to cracks when fed a steady diet of 125 grain fireballs. It seems to tolerate the slower 158 grain loads.
If you are looking for a shooter, the best choice is probably a 4" 586, or the stainless version, 686. It's heavy enough to handle full loads without bruising your hand, long enough to give a good sight radius at the range, and small enough to conceal. It is much sturdier than the 19/66 revolvers. The full length lug makes the 6" too barrel heavy, IMO.
The 4" 686+ (7 round cylinder) is my favorite revolver to shoot, but I also have a 3" version which is easier to carry and nearly as accurate, and has a full length extractor. The 2-1/2" version has a shortened extractor. That's possibly slower to reload, but I don't find that .357s have much tendency to stick.
The 27/627 is an N frame, much larger than the 686, and harder for me to deal with DA shooting. The 686 has the same grip and reach as the K frame 19, and a better fit for smaller hands.