Being very familiar with both, I would stay w/ the M&P. My reason are thus;
*Both are very decent weapons, but with prolonged firing, I have seen striker pin damage in the FN. Not enough to put the weapon out of action, but to me, it was a concern. It appears to be caused by poor parts engineering to me.
*It is very hard to soften up the trigger pull on a FNS. They are stiff from the factory, and remain that way pretty much from then on. No aftermarket support about this problem so far, at least none I am aware of, and no easy way to fix it.
*The magazine release system in the FNS is lacking. While the button is ambidextrous and easy to use, the latch itself is too small for the application. The stop on the magazines are easily damaged and prone to allowing a magazine to fall out. Look closely and you will see what I mean.
*The FNS appears to be a mostly, if not all, MIM parts gun. While almost every firearms manufacturer now uses lots of MIM parts in their firearms, the FNS seems to be almost all MIM parts. Does MIM work? Yes, it does, and FN seems to have embraced it fully. Not sure I care for that, and I have not heard of any endurance testing of FNS pistols as of this time, nor am I aware of any Law Enforcement agencies using FNS pistols. Of course, I might be wrong on both of those accounts, too.
*Poor to no aftermarket support, as has been said. There is just almost nothing out there for FN pistols as of yet. And just no resale value at all. I also think that MSRP from FNs is too high, given the kind of pistol they are and that is part of the reason they do not sell well.
Do I like the FNS as a basic pistol? I really do, it is a neat gun. But while I have had several occasions to purchase an FNS, due to all that I have mentioned, I have chosen not to do so. My close friend did purchase one and being his shooting buddy and personal Armorer, these are the things I have discovered in using his pistol at length.
The M&P IS a better choice, period.
As always, YMMV. Good luck.
