I was fortunate enough to be able to buy both the LCR 357 and the M&P 340 ( not at the same time). The past 2 weeks gave me some time to evaluate the pros and cons of each.
Please keep in mind this is only my opinion.
Concealibility is about even. The Ruger has the Hogue tamer grip so its slightly bigger, with this combination the edge is with the Smith. The LCR has a boot grip available, with that grip it would tie .
Weight... The Ruger being stainless is heavier 17.1 oz to the Smiths 13.5oz.
Trigger... The Ruger wins this one. Its smoother and has a lighter pull. I think the LCR has 8.5lbs vs the Smiths 12-14lbs.
Finish.. No question here the Smith. Its a more expensive gun but it shows, I'm sure the Scandium also adds to the price.
Shooting.. I found the LCR more comfortable, the grip is better and it isolates the recoil better. Even shooting 357 magnums was tolerable but I would not make it a habit. The Smith with the smaller boot grip was slightly more punishing.
Ammunition... Practice was with standard pressure 38 130gr FMJ WWB
Defense I used Speer Gold Dot 135gr short barrel 38+P
I also compared several 357 loads:
Speer Gold Dot 125gr JHP,
Speer Gold Dot 135gr Short Barrel JHP
Fiocchi 158gr Semi jacketed HP
Recoil was about the same for the GD 125 Gr and the Fiocchi 158gr.
The GD 357 135 gr short barrel was a nice surprise, its not as punishing as 125gr and 158gr magnums. It also felt a lot hotter than the GD 38+P. In my opinion I thought the GD135gr SB 357 was a perfect carry load.
Ballistic numbers from Speers LE site
GD 38+P 135gr SB Muzzel 860ft/sec125gr Energy 222ftlbs
GD 357 125gr " 1450 ft sec " 584ftlbs
GD 357 158gr " 1235 ft sec " 535ftlbs ( I did not have Fiocchi Spec. GD listed)
GD 357 135gr SB " 990ft sec " 294ftlbs