LCR 357 or M&P 340?
The 340 is a little lighter weight. Good for carrying, not so good for shooting it.
The grips are a little more compact on the 340. Again good for carry. The Tamer grips on the LCR are going to soak up more recoil. Again better for shooting it.
The M&P340 comes with an XS 24/7 Tritium Front Night sight. The LCR has a pinned on front sight and for around $50 you can have the same sight on the LCR.
The LCR357 is around $275 cheaper. With the same front sight that would be only about $220 cheaper.
The factory trigger on the LCR will probably be a little better out of the box.
The M&P340 may be chambered in 357 Magnum, however it will be no fun at all to shoot with 357 Magnum ammunition. The LCR 357 will likewise be a hand full, but way more manageable than the 340.
The M&P 340 is a better looking revolver than the LCR 357.
I was looking at both at one time. I went with the LCR 357, it was a better value, and a more shootable platform with the factory grips that came on both.
I could not convence myself that the M&P340 was worth $725, when the LCR 357 was $450