Of all the rounds (calibers out there) the one where the biggest improvements have been made over the past 30+ years is the 9mm cartridge.
(I've had one guy actually try to tell me that the 9mm now 'exceeds' a .357 magnum in performance, which I don't believe for 1/2 second as I grew up on .357's...but they have come a long way.)
The caliber war can and probably will be discussed/argued for decades to come...but I don't think anyone can argue that the 9mm cartridge has come a long way in performance improvement during the past 30 years.
While, I personally think there are a few advantages to other cartridges...the one advantage 9mm has going for it is smaller size (diameter) allowing for more rounds in a similar sized magazine as compared to .40 or .45...and, with center-mass shots, the 9mm will do the job (barring the shooter gets center-mass hits...which is always questionable in a dynamic situation.) Having a larger number of rounds in a magazine can make a difference in a life-n-death situation...9mm costs less...and, for many, control is an issue that has to be considered, especially with 2nd and 3rd shots.
Personally, I prefer a .45 acp...but that doesn't make the 9mm caliber 'bad'...I just prefer the way the .45 feels when I shoot it...recoil is manageable, accuracy is excellent, and there's something about that big 'ole ball working in conjunction with a thing called kinetic energy that is comforting.
I think one of the bigger factors, and one that is not often discussed, is bullet weight (grains) as the heavier bullets will generate more dispersed (kinetic) energy and also generates more 'momentum' (forward force) than a lighter bullet will generate. Take the .22lr for example...it's zinging along at a rather fast speed, but has no weight to it so even when it does penetrate, it'll bounce (ricochet) off just about anything and doesn't have enough energy (momentum) to penetrate much of anything either (a good paperback book'll stop it pretty easily.) Whereas the lighter bullets have a tendency to bounce (ricochet) the .45 has more momentum to 'push-through' and continue in a relatively straight line. While the 115 grain 9mm bullet can be pushed out to 1350 fps (or even more) and generates up to 465' lbs of energy dispersed...but it takes a higher velocity + bullet expansion to achieve what a 230 grain .45 acp will accomplish traveling 400 fps slower.
When the .40 was first developed (shortened from a full-sized 10mm round) it definitely had an advantage over the 9mm (force x penetration x bullet grain) but as the 9mm has continued in it's improvement over the past 30 years (and especially over the past 10 years) it's simply closed the gap on the .40 and the .45 acp.
Will the 9mm ever 'catch' the .357SIG??? Hard to tell...the .357SIG has a definite advantage sitting on top of that necked-down .40 casing that allows for more powder + 'bottle-necked' focus to the energy created, pushing the .355 diameter bullet harder (faster) than a standard 9mm casing...I think it'll be a while before the 9mm catches up with the .357SIG round...especially since one can take advantage of the 9mm bullet's expansion improvements and sit it on the .40 casing and stay ahead of the 9mm itself.
Even though I prefer the venerable .45 acp round, whenever I do wanna shoot a 9mm bullet...I simply take it and mount it on top of a necked-down .40 S&W casing and shoot it that way...in that configuration, it then feels very similar to the .357 magnums I grew up with.
