I have an M&P 40 I enjoy shooting and it feels good in my hand. I also like shooting my Glock 17. I really couldn't tell the difference in recoil. My only experience with a 357 was with a S&W 686 with a 6" barrel. All I remember is it was LOUD and I preferred shooting the .38 specials in it.
Get the .40 cal m&p, and then the very cheap sixty dollar .357 barrel for it. The mags work for both, and if you end up shooting it in competition, they will require you to shoot the caliber marked on the gun.
The story with the triggers is....stock trigger is really pretty bad, pro series is a tad better, and if you put in a Apex kit it becomes pretty good.
I went ahead and got the .357 m&p just because it was a good deal made a trade no money. I am glad you said something about having to shoot what is on the gun in matches I didn't know that. I was thinking about buying the .40 barrel for it but I have a .40 so I might just wait and see. I haven't shot it yet.
I have an M&P .375c but I have never shot the sig barrel. Came with a .40 barrel as well and that is what I loaded up. I have a few boxes of .375 sig and want to take it out for a spin. I have heard that the sig round is quite snappy in the little pistols.
Oh and about the trigger... I was ready to sell or trade the compact after a few mags. It was horrible. I actually took it apart to look for the sand that had to be in there. The trigger was so gritty that I stopped carrying it until my Apex sear came in. Took just a few minutes to swap and then a few hundred dry fire rounds and I was good to go. Brought the size of my 30' shots to almost half of what they were.
I have an M&P 9mm that I carry frequently. One thing that I really liked about the interchangeable backstraps was that I could stipple them without risking ruining the frame. Made a huge difference. I typically run the smallest backstrap for CC, and the added texture really helps.
I have the M&P 9mm. The Apex sear is very good. You can also search the web for instructions on how to modify your sear. I modified my sear with good results but the Apex is better.
Nice grip shape for my small hands.
I use grip tape for a little more secure grip.