I love this!
686
Model 27
Model 66
Model 19
That's like asking guys which is better, blondes or brunettes!
Jokes aside, they're so different you have to ask yourself what, exactly, are you going to do with them.
I have never owned a M66 but I have owned 3 or 4 M19s, 4" and 2.5". They're wonderful guns, will handle any .357 load I ever tried, but they're not necessarily the strongest tool in the shed. But for an easy shooting, packing pistol, K frame .357s are hard to beat. Since the main difference between a M19 and a M66 is blued steel versus stainless that's more a matter of taste as far as I am concerned, unless you're on a boat, in which case stainless is the better choice.
A M27 is a tank. Omitting the obvious with respect to the checkering, and other luxury items, it's an N frame tank. If you're any kind of recoil sensitive this is the gun that tames all of the .357 Magnum recoil you can find. But if you're thinking about carrying it, well, just remember it's tank, and damned hard to conceal.
So, that leaves the M686. Barrel length is always a factor and you don't say what your purpose is but the M686 will handle every .357 Magnum you feed it and in almost any barrel size except 6" it's not impossible to conceal and certainly not too difficult to carry.
When you just love revolvers it's always hard to say which is best or your favorite but until my twin brother gets his hands on my 3" M 686+ I think it's the winner here.
He does want it soooooo badly!!!
This M19 is no longer with me but it's a stunning gun:
This M27 Classic, as modified, is so wonderful it's hard to describe but it IS a tank!
These M686+s are way up on my favorite list:
2.5"
3"
4"
That full underlug, I dunno, it's just so racy looking to me!
The best? VERY personal, very, very personal!