Can't speak on the S&W, but own/owned the K6s & King Cobra (and an SP-101), all 3" barreled versions. Examples of one, so take with a grain of salt, ymmv, etc.
SP-101 went back for a repair early on, but was back in about a week & went through several thousand rounds without issue. Took awhile to get proficient with it, & the trigger had a lot to do with that. Wasn't horrible, but wasn't very good either. Didn't dislike it by any means, but never really meshed with that revolver. This was in the mid 2010's, fwiw.
Not a good experience with the King Cobra. Went back for light strikes, sticky ejector rod & a timing issue. Timing & ejector rod issues eventually corrected, but light strikes persisted. Did not shoot it well, though in fairness that's likely a symptom of just not fitting my personal preferences in grip, balance, sight picture etc. Did have a good trigger. Made mid-2020, fwiw.
K6s DASA is now my carry gun. No problems at all out of the box. My favorite trigger & sight picture of the three. Most comfortable of the three with magnum loads- more a statement on how well it fits me personally than any magical ability to absorb recoil. I get back on target for double taps faster as well, probably because I'm able to get a higher grip on this revolver than with the other two (again, a good fit for me, but we know one size never fits all).
If it sounds like I'm a fan of the K6s, it's because I am
. It's not perfect though:
- Wish they'd used the extra barrel length to increase ejector rod length, uses the same one as the 2" models. I've not had any trouble (yet) ejecting cases when done with authority, but making it full length sure wouldn't have hurt anything.
- Kinda wish there were different front sight heights available. Like the fixed sights for a carry gun, & mine are right on with 158 grain loads. Noticeably low with 125. Carrying 158's for now, but haven't settled on that long term. If I go 125, would have to either file down the front sight or spring for the (expensive) adjustable sights Kimber sells.
Those are the only two nits I have to pick with it, and one is correctable if I so choose. Can't comment on long term durability; so far so good after 850 rounds. It does appear to be very well made, with good materials.