Like nearly every other single issue that gun folks argue, battle and carp at each other over, this one is simply an issue of preference. I get tickled when I see a mini mob online gang up like a feral dog pack and attack some poster because he dared criticize or 'not like' whatever their pet inanimate object made by (insert name of favorite here) gun company.
I've been robustly active in firearms as a hobby since 1989, been using them professionally since 1991. I have used Sig Classic P Series very extensively, and S&W 3rd Gen's actively. All I can tell you is my preference.
Smith & Wesson 5906
The S&W 3rd Gen's are built like M1 Abrams tanks. They'll feed rocks. There were the first pistols I ever came across that had Novak sights, which have come to be one of my favorite styles. They normally have a really heavy DA trigger, but alongside that there's usually an outstanding follow up SA trigger, and are combat accurate. They are heavy, but that weight keeps recoil down.
The 5906 (and 3rd Gens at large) dominated the LEO market in the 80's and 90's, so if the use of a pistol by large LEO agencies appeals to you as an endorsement, then the S&W had that in spades.
Cons? I don't care for slide mounted safeties, as I have very large hands and when I grab a slide and do a very robust slingshot, those safeties go right into the meat of my left palm and that doesn't feel wonderful. Also, the black Delrin one piece grips are way too slick, but a set of rubber Hogue's cures that quickly. The mag safety is a foolish idea. I get the argument for it, but I don't buy it... I want to be able to fire it *right now* if need be. The 'what if' of being shot by my own gun involves so many variables, it doesn't to me justify creating a condition where my gun cannot fire. I still buy 3rd Gens, but if possible I look for ex-LEO guns that had that feature ordered as 'disabled' when they were manufactured, as I don't want to explain in court why I disabled a safety myself.
Lastly, they simply don't make them anymore. That's a bigger deal when considering current or future supply of spare parts, if one were to break. Also, stripping the pistol down to all component pieces and reassembling it is not exactly as easy as putting together a Revell Snap-Tite model....it's a bit complicated and not for beginners.
Lastly, they are becoming collector's pieces, not so much carry pieces, now. So options for holsters (and perhaps in a few years magazines) will become less plentiful.
Personally, I think they're the last great pistol S&W has made; there is absolutely nothing they've made beginning with that Sigma disaster that I am remotely interested in. I'd only take some of their newer Tupperware junk if I got it free, but only so I could use it as trade bait. Harsh, I know, but that opinion is colored by how great the 3rd Gens were, and how not-great Smith's follow up offerings have been.
Aside from the aforementioned dislikes, if I were to have a 5906 on my hip loaded with very hot, lightweight 9mm JHP's, which I prefer, and an extra mag, I would not feel under-gunned or out of a fight.
Sig Sauer P226
The Sig's are, to me, world beaters. I greatly prefer DA/SA (although I'm a bit of unicorn in that I do like their DAK system) over striker fired pistols of any kind. I'll stick to talking about the P226, because frankly the P22X system is the same whether you're carrying that one or a P220, P225, P228, P229, P227, P224, P239, P245 or whatever other variant (like the M11/A1). They all run the same; the manual of arms is identical.
My experience is largely with the P226 in 9mm and .357 Sig, as I carried it for a longer period of time and over the decades I've found that whether a particular P226 was a West German model, a Legacy with the shorter stubby extractor or an E2 with the newer 'surfboard' extractor, they were all balls reliable, damned accurate, rugged and simply fantastic pistols. They have some of the finest barrels in the industry with match grade accuracy far exceeding normal combat accuracy.
There is no safety on the slide, just yards of great big steel real estate that my fat paws can grab violently and slam without getting chewed up. They point very naturally for me and feel like they're custom made to fit my hand. Grips are easily changed from factory plastic, to Hogue rubber grips or a variety of G10 textures, or even fancy wood for the weekend BBQ.
Additionally, the SRT kit makes the Sig the equal of the S&W in terms of SA pull. The decocking lever is instinctive and, unless one demands a safety on one's pistol (I don't), it safely takes the pistol off the cocked SA condition. It's a very easy pistol for student shooters to learn on, too. Lastly, breaking a P226 down to the smallest components isn't as intimidating as many other pistols. Is it as easy as some modern Tupperware guns? No. But once one does it a time or two, it becomes clear that it really isn't very hard, at all.
There is a huge variety of finishes and style available, although some are now discontinued. Some are really cool, some are a bit fey and admittedly, some are just silly.... basic Nitron, MK 25, Legion, Equinox, Elite, Platinum, Scorpion, etc., etc., etc. And you can get 9mm, .40 and .357 Sig. If you want what is essentially a P226 in .45 ACP (the difference is dimensions is so small it's negligible), get a P227... heck you can even get one of those in a smaller Commander size with a rail (Carry) or smooth (SAS) version.
Again, if LEO (and in this case military) use stands as an endorsement to you, the P226 has worldwide credibility. The number of agencies, armies and units that used it are impressive. Personally, my own experience (and plentiful ammo and shooting afforded to me by working as a full time LEO for 35+ years) allowed me to truly wring out that design over a long period of time, and I found that it was consistently reliable and accurate... and to me consistency across numerous decades and multiple samples of the same model is far more instructive than any one particular pistol doing extremely well in some torture test. A sample size of one means nothing.
One cannot ignore how many LEO agencies used it, including it's derivatives, over the last 40+ years. Also, I have to say that long term testing was far more valuable info to me personally than whichever military ops units may have carried it. I don't get hung up on the Navy SEAL thing about the P226. Even in that rarified atmosphere, it still comes down to preference. Individual SF guys can choose the individual pistol what they want, or so I've been told.
Unpopular opinion, but I don't really care what pistol any SF group uses or any particular SF online personality uses or endorses....99.9% of American pistol carriers or LEOs do not use them in such harsh desert or jungle overseas environments, anyway. Besides that, pistols themselves mean little to any military combat unit, from what I know, as they live and die by the rifle they carry... pistols are of very little thought unless it's a dire emergency at that's the last option. Pistols are largely easily portable defensive, not offensive, weapons.
Having said that, one cannot ignore that so many military units used the P226 for so long. And if not for a few bucks difference in the cost of the overall maintenance package, it would've beaten the Beretta M9 and become the default pistol of the US military.
Cons? Even today they have a heavy DA trigger, but the older WG's are far worse...the newer the 226, generally the better the DA pull. They are pricier than other standard pistols, but I don't think this is as wide a margin as it used to be. Some folks complain about its 'High Bore Axis'. I disagree, and will do so while laughing about it.
>>> Side note: IMHO, 'bore axis height' is about the single most overrated, over discussed and irrelevant topic in handguns one can waste bandwidth on. Many revolvers that were used for decade upon decade by professional lawmen that had "high bore axis" were employed very quickly and effectively, because they were correctly trained on those guns. Simply getting proficient with whatever pistol you intend to rely on by training with it extensively, eliminates the issue.
If one thinks that a 'lower bore axis' is key to shooting faster, to the tune of a fraction of a second, maybe one should think more about target identification, shoot-and-evaluate, shooting with maintained control, and less about emptying out a high cap mag as fast as one can. Quick controlled accuracy provides greater results than trying to 'game' one's way into simply being a faster and faster shot. If the difference in slide height leads one to believe that those fractional difference are a life and death matter, then one either hasn't trained enough, is listening to many online tactical larpers or they're watching to many John Wick films. Just my $00.02 on that. <<<
Bottom Line:
Of my preference (and mine alone), the P226 wins big over the 5906 because: the P226 is/has:
• More ergonomic
• More accurate
• No manual safety on the slide
• Simpler manual of arms
• Intuitive decocking system
• Greater availability of magazines and parts
• Greater availability of sight/holster options
• Still being made and much more widely available
• Greater diversity of calibers and frame styles
• Consistency of longevity over four decades
• Continuing history of worldwide use in harsh environments
I still really love my 5906, and all the other S&W 3rd Gens in my safe, but sadly they are slowing becoming very interesting pieces of firearms history, not daily carry defensive weapons.
I would be over the moon if S&W righted their ship and stopped using two piece revolver barrels, stopped putting that inane lock on every one of their revolvers, put the damned firing pin back on the hammer where it goes, but most of all, if they went back to making limited runs of 3rd Gen pistols... specifically the 5906, 6906, 1006 and yes, even the 1076.
It would be glorious.