It's important to denote that because the Ruger frame is larger, that does not make it stronger or more robust. It's larger because it's more cheaply made, not stronger. This is not an opinion, it's a fact. This is the dirty little secret this thread has been too polite to talk about so far, or perhaps folks aren't aware of? But since you've brought the cat out of the bag...
S&W uses forged frames, and Ruger uses investment cast ones. One process is much more expensive, and ounce for ounce and square inch per square inch, yields a stronger finished steel product. Further heat treating and finishing increases the difference. A S&W will be less bulky for the same strength as a Ruger. This is one major reason the K and L frame S&Ws, in my opinion, handle, point, and are generally more controllable than the Rugers. Go to a firing range that rents guns, or a store that has both, and compare the handling and pointing characteristics.
Here's one anecdotal point - for my last-ditch bear gun, I don't carry a 4" Ruger Redhawk - it's big, it's bulky, it's annoying to me to carry (I'm only 5-10 on a good day). It weighs 47 ounces empty with air-weight spongy hogue grips. I carry a S&W 629, with a round butt in 3". It weighs in at 37 ozs empty, with large hardwood (facotry) combat grips. Over a 27% difference in weight, even handicapping the S&W with the wood grips. I can get the 3" S&W to handle the same loads as the ruger - and I occasionally shoot 320gr LFNGC bullets from Double Tap and Grizzly that move at 1200fps. This is not a light load. The density of the steel in the 629 let's me get a more controllable package in a smaller gun of greater strength. The wood grips, with a large and solid contact patch and rigid finger grooves, vs. the spongy ones on the Ruger, contribute to this. Thes are both factory delivered guns, not carrying a single accessory on them. You have to look at more than weight and it takes a good grounding in physics to explain all the implications of angular momentum, density, etc. and how that translates into felt recoil. Or get a couple of boxes of bullets and go shooting, it'll become apparent pretty fast! One of these guns is quite a bit more expensive than the other, but they both do the same basic thing.
Another way to look at this is: why is a S&W always more expensive than a Ruger? They are located nearby in the same geographic and economic region. Raw material costs, labor costs, administrative costs, etc. are going to be identical. Marketing and distribution costs are probably the same, too. It really can only come down to the one variable we can see that is different - construction methods and the labor and equipment involved.
As for Ruger "defining" reliability, the cheaper construction methods generally result in more QC problems in owners' hands than S&Ws from what I have anecdotally collected on this and the Firing Line Forums. Both do offer a life time warranty, so you won't be left out in the cold in either case. I hear of more Rugers making an immediate trip back to the factory than I do S&Ws (it does happen to them, too) - and I also hear it always comes back working correctly.
The L frame S&W revolver was specifically designed to handle ANY .357 round that could be crammed in it. It was a beefed up version of he K- frame, introduced in 1899 long before the .357 came down the pike. A compromise of shoe-horning the .357 into the K-frame in the 1950s created a medium sized gun more powerful than anything else in the world, and later developments of small, even higher velocity bullets (125gr and 110gr rounds in a .357) did result in some failures. Used with 158gr or larger bullets, the K frame 19 and 66 models, or the 65 above, will last a lifetime (note the "K-frame" models are slightly smaller than the 586/686 we are talking about here).
The result, however, was the L frame 586/686, designed to handle the .357 in a reasonable sized package, retain the balance and handling S&Ws are known for, and take any round you could put in it. It does not rely upon cheaper casting and "over sizing" to accomodate for the necessary strength, like the Ruger does.
So, if we want to go by the original poster's "Highest Quality" question, the design parameters and the build methods of the S&W make the Ruger look like an East German Trabant. Well, more like a Mercedes vs. a Volkswagen - both excellent, one just a bit more refined and pleasurable.
I don't want to start a war about Ruger vs. S&W. I think Bill Ruger was a great firearms designer, and did everyone a great service resurrecting the SA via his Blackhawk, and has given experimental shooters great platforms on which to develop new loads. Important stuff.
Each company does things a little differently, and that's good. I won't say "I won't buy a Ruger" - heck I have bought two in the last seven months.
