I'm a big an M&P fan as anyone, but DON'T discount the FNS9C. I own a M&P 9C and have worked on/shot the 9FS. They're M&Ps, no issue with either. The 9C is chunky, but that's to be expected with a double stacked mag and short grip. My 9C is apexed and also has a stormlake barrel. It shoots okay, but the short, stubby, chubby, grip takes some getting used to depending on hand size. It is what it is. People probably said the same thing about the 6906 vs. 3913 back in the day.
Picked up a P320 compact in 9, quality firearm but thoroughly unimpressed. Shot decent, trigger pull is "eh" and not near as good as an M&P with an apex kit considering you typically pay noticeably more for the Sig. The P320 is noticeably larger as well, particularly the slide. It's currently on my short list of "to sell" given the opportunity which is something I typically don't do.
I own an XDS45, very accurate but finicky about ammo just not overly pleasant to shoot. Trigger pull is typical XD, okay but again not as good as an apexed M&P in my opinion. It has long since been surpassed by my Shield 45.
The LGS had FNS9s on sale for a really good price considering it came with night sights and 3 mags. Had been thinking about a full size 9 for a while. Didn't take much persuading to walk out with it. My M&Ps have the external thumb safety, The FNS came with an ambi mag release AND safety. Very accurate firearm, well made, and a true sleeper. Out of the box the trigger was a bit stiff. I polished a couple points, which helped some but ended up sending it out to a gunsmith who works on FNSs. I think the cost was $70, which included shipping back. He was slow and I had it back in like a week. Well worth the $70. I'm as big a M&P fanboy as many on here but would take the FNS9 over an M&P9 and that would include the FSN9C. The only downside is probably the cost of spare mags. They're a bit pricey.
I believe I've narrowed it down to 2. The M&P 9c and the Sig Sauer P320c. Definitely going to go FDE no matter which one I choose. Just wish there was a range around here with the Sig to shoot.