The 627 is on the same larger frame as the 44Mag, and is an eight-shot 357
. It's also a "custom shop" gun so the trigger is generally very nice, and it uses moon clips for rapid reloads. Pricey, big, but otherwise really dang cool. The only S&W that I'd consider buying, myself.
The 627 is generally considered the finest competition revolver available as long as you can do that sport with the .38 or .357.
Like the .44Mags, the 627 is an "N-Frame", the largest current S&W platform.
The 686 is built on a smaller frame, and is available either as a six-shooter or seven-shot (the + model). It's a better carry gun, but as it's an "L-Frame" it can stand a steady diet of hotter loads than the next size smaller...
...the "K-Frame" six-shooters such as the model 66/65. The K-frame was originally built for the .38Spl, and later beefed up for the .357. Still, too much hot ammo can eventually wear these prematurely, which is why the L-frame was developed.
The J-Frames are the smallest, in .38 or .357 they're 5-shooters.
OK?
If you want a carry gun that you'll shoot mostly .38 through, the K-frames with a 2.5" barrel are great. Ted Nugent packed such a thing all the way through the height of his touring days in the late '60s/early '70s (see also "God, Guns and Rock'n'Roll"
). If you're going to do more range play with hot ammo and still have something that can be carried, that's what L-Frames are for.
(Ruger fan note: the GP100 is basically "L-Frame sized" and eats out of the same 6-shot speedloaders. The now-discontinued Security/Service Six series was more or less "K-Sized", the Redhawk is more or less "N-sized", the SP101 is a massively beefed up J-class gun and the SuperRedhawk is a beefier frame than anything S&W has *ever* made, although there are rumors of S&W prototypes designed as "SRH killers".)