Almost "who knows"....
I've been carrying for about 42 years.... My first "real" handgun (some cheap junk not counting) was a Charter Arms "Undercover" .38, circa 1967. I probably should have spent the extra ten or twenty bucks for a Chief's Special, but my budget was kinda slim at the time.
I was able to handle a couple of S&W K-frames back then, and when I needed a "uniform" gun (I'm a semi-retired rent-a-cop, among other things), I decided an S&W M19 was a good choice. (.357 magnum.) I couldn't find a 4" - the Military was buying everything, but a friend found me a 6". I'm big enough that it didn't look too silly.
Later, when a concealment gun became a good idea (the Charter stayed on as a BUG, but I couldn't hit anything with it; still can't!), I picked up an M10HB, which is the same K-frame in 4", with a heavy barrel - pretty much the same barrel that the M19 uses. Wearing a 4" K-frame for concealment sounds nuts, but in those days printing didn't really bother anybody, and there were no restrictions on where I could carry other than the jail or a courtroom, and then only if somebody was checking.
I was exposed to Colt guns at the time (as well as Taurus and Rossi) and felt that spending the extra few bucks on the S&W's beat the clones, and that the Colts just weren't what I wanted....
Although I kept carrying, I stopped shooting, more or less, until 2004. Having to get a CHL put me back on the range (with that M10HB) and a realization of how much fun I was missing.
Ended up joining the local Rod & Gun Club (nice ranges) and buying a lot.... I'd picked up a PPK/S and an M39 way back when, and inherited a Combat Commander. The latter got me into 1911's big time.
About a year ago, S&W was doing a magazine rebate, and I wanted a .40 just to play with - a range gun. The M&P40 Full Size fit the bill - not a "target" gun, but a good shooter, reliable, etc. I can see clearly why it's a "service" gun, like my old M10, too. I occasionally carry a full sized 1911, and could get away with the big M&P, too.... (I have carried it a few times.)
Then, much more recently (and with yet another magazine rebate), I swapped off a PPS40 (the PPS9 is a super gun, but for me, the .40 is awful....) for an M&P40C. The idea was for something that I could wear around the house without pulling my jeans down.
I bought an XD9SC for my daughter a few years ago. She just didn't want it. Nothing really wrong with the gun, other than it being kind of bulky for a 9mm, but the super-short barrel made for a lot of smoke and flame. I swapped it for an M&P9C a few weeks ago. It's hers if she wants it. Meantime, I'm "working it in". (She's talking about moving to New York.... Ooops....) No rebate this time, but I wanted out of that Springfield. So far, it's excellent, but does appear to need to be shot in a bit. (The other two M&P's were 100% immediately.)
All three M&P's have DCAEK kits in 'em, and RAM's in the .40's. The RAM, IMHO, is a YMMV thing. The DCAEK kit gives me a feel that's very much like my old S&W wheelguns, which were about as good as you could get as "production" back before quality went away. They also feel like my two Para LDA's, which have a similar feel.
More "damn, that ought to be fun" than research for the first one. The other two M&P's just sort of fit....
I hate to admit it, too, but the M&P's are also "airline travel" guns. Unlike my 1911's, they're inexpensive, and I don't have any real emotional ties to them. IOW, should the airline lose one, hopefully during the final leg of a return home, the insurance check would probably make me feel good enough.... If you actually use a gun, it's likely to vanish anyway, but locally, at least, I have a shot at getting it back. If I'm visiting somebody 1,000 miles away, that gets a lot less likely....
'Course, I'm old enough now that a drive of more than a couple hundred miles is something I'd prefer to avoid, and the "Security Theater" we now go through to fly is going to (along with budget issues) keep me home a lot more.... But that's another story.... I have a sister in TX, and a brother-in-law in FL....
Regards,