I voted FN-9c, but, generally the decision between S&W M&P, Glock, FN, Ruger, etc. are pretty much splitting hairs. There is very little distinction in the handgun market nowadays. I think the FN has a safety that you can use or not, which is a nice touch. For example, if it will be kept in the glovebox of a car with a round chambered, then a safety could be a plus...not something done in military or police circles, but a situation a civilian could encounter.
As far the Glock, I've owned them, maybe it was revolutionary 36 years ago, but it seems pretty average to me. Average ergos, I have a high grip, so I'll sometimes get bit by a Glock slide. Average accuracy, they don't shoot as fast or accurately as some of my metal framed guns, I shoot a CZ-75B much faster, for example, but that's a heavy gun. They're generally cheap, so that's a good thing. A decent middle of the road choice, not good at any one thing, but not awful, either. The light trigger, no safety thing spooks more people that gun board posters would like to admit, most hardcore shooters I know seem fine with it, but many of the casual gun owners I know usually don't carry them chambered. Right or wrong, that's what a lot of people do...
As far as aftermarket support, all that really matters are holsters. I used to say night sights, but a lot of companies will add these to just about any pistol, like Tooltech Gunsights. Most of the stuff they sell from aftermarket barrels to impractically long mags can be fun, but aren't that useful.