Well, there's the M&P9 shield and the LC9. To me, there's enough difference between the two, they really aren't in the same catagory.
The LC9 feels slimmer and will carry with less intrusion than the M&P9 Shield. I'm probably one of the few that actually like the LC9 trigger, albeit long, mine is super smooth and I'm very accurate with it. The M&P breaks much quicker and is a great trigger, but it's really hard to compare the two here.
Using the flush fit magazine, as it is now, I prefer the feel of the LC9 in my hand. While the grips are similarly slim, the grip on the M&P has more depth, making it feel a bit slimmer, somewhat out of proportion compared to the LC9.
Recoil between the two seemed nearly identical. To keep things even, I shot some of my 115 gn Rainier plated reloads in both. Already knowing the LC9 shot them well, the M&P had no trouble with them at all. Shootability felt better with the extended magazine in the M&P and gave me a full grip.
Fit and finish of my M&P seem to be excellent, no pitting anywhere that I could find. The sight's dots are a bit bigger on the M&P and are very nice for staying on target. Honestly, I'd heard about the 'audible' click with the trigger reset, but I didn't notice it.
I tried the M&P in the Desantis Soft Tuck holster that I use for the LC9, and while I was able to force it in, it's just not going to work as the bulkier barrel end just grabs the holster and hangs on. I'm thinking a form fitted leather or kydex holster will be the way to go for the M&P due to the blocky slide. It doesn't lend itself well to sliding in to a holster such as the Desantis Soft tuck as much as the LC9 with it's slender tapered slide.
The M&P really does feel and look like it's big brothers other than being much slimmer in the grip. It's definately a keeper and gives the impression of being more work oriented than the LC9.
The take down lever stays in place, as opposed to the take down lever on my M&P40c.