I have a number of S&W K and L frame revolvers to choose from.
As well as some Ruger six series:
While I like the Model 66 in many ways, if I could have just one it would be my 3" 686+ for a number of reasons:
1) A Model 686+ is only about 2 oz heavier than a Model 66 of the same barrel length and has the same grip size and trigger reach. And it's still only a 35 oz handgun.
2) the 686+ offers 7 rounds rather than 6 for the Model 66, and like the 66 it's heavy enough to shoot well with full power .357 mag loads and still light enough to carry all day.
3) The 3" barrel is short enough to readily conceal and long enough to be reasonably ballistically efficient with the .357 Mag, particularly with proper load selection.
4) The L frame 686+ is much more durable than the Model 66. A small price to pay for a couple more ounces in weight.
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The Model 66 wouldn't be my second choice either. The Ruger Speed Six and 2 3/4" Security six are also much more durable than a Model 66 and split the difference weight wise between the 66 and 686.
When I first worked in law enforcement I purchased a Service Six (pictured above between a 6" Security Six and 2 3/4" Speed Six) because it was much more affordable than a S&W Model 19. But I quickly noted not many officers carried a Model 19, they were more likely to have a Security Six or a Model 28.
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On a related note, this morning I reorganized the "ready" gun safe, the small one with the rifles and handguns I use on a regular basis. The two revolvers that made the cut were my S&W 3" 686+ and my Kimber K6S. The K6S does a nice job when the 686+ is just a little too large.
IMHO Kimber may have gotten this one right size wise. It's a bit bigger than the J frame and very close to the SP101, but offers 6 rounds. Once you put a little larger grip on it, like the SP101 it becomes a tolerable to shoot but easy to conceal revolver.