I started out in LE with an issued S&W M15 Combat Masterpiece .38, and with a lot of work managed to become an excellent range shot. What's wrong with that statement? Right - no real combat training with live ammo. When I transitioned to an autoloader (Colt 1911 .45) I had a lot of new learning to do, habits to break and gain... no more speedloaders, no pockets of brass (I was taught to pocket my revolver brass), no dropped loose rounds when I ran out of speedloaders...
Then, after years with single digit mags and the occasional hang-fire because of weak springs, I had an opportunity to test a 9mm by Springfield Armory, and shortly thereafter, a S&W ... after the beefy delivery of the .45 the 9mm felt weak, and reports came in of men shot center-mass who managed to continue resisting and sometimes managed to injure or kill the officer involved.
Then the .40 hit the street. Single-hit knockdown, almost triple the capacity of the .45, lighter than the .45...
You can find as many opinions about individual weaponry as there are weapons... personally, I would rather carry a good DA autoloader that fits my hand well and I can shoot straight than any other option.... because, when all the arguments are over, what any officer should use is what gets the job done for them and falls inside the individual requirements of their department or agency for duty weapons.
So... do your due diligence. Talk to other officers.... Test-fire weapons, try them under the greatest range of conditions you are likely to encounter, varying light and weather, off-hand, standing, after 1/4mile run, ... the greatest weapon you'll ever have is the one that floats in your head. Make a connection between your brain and any handgun, familiarize yourself with all of the idiosyncracies of it, and practice/practice/practice. When you have put a few 1000 rounds through your piece of choice, and have practiced until you feel qualified, then hit your Hogan's Alley and fire under stress. Bottom line: what works for you is what you should carry.
In New York , we train as we may fight. You are only as good as you are proficient with your weapon of choice. Whether it be a Kimber, Colt, Springfield, or whatever flavor of the month weapon thats come out, proficiency is the name of the game. Just my opinion, and we know what saying accompanies that, but, a 1911 unde duress as you'd be put under at a response to a threat, requires one to be cool as a cucumber. It's a Thinking Mans weapon. A striker fired weapon such as a Glock, or Springfield will go a long way when you're under the gun. Its' use is second nature to most of us, making it quick, agile and deadly at the ranges we'd encounter under duty situations.
STI Duty One are great weapons unfortunely i traded it up for a Sprinfield TRP Operator . I still own the STI spartan in 45acp it is a great system even though it is their lower end model the problem i would recommend for STI's is getting a better finish such as Crekote or another good duracoat finish but all in all the Duty One or Spartan has not let me down. I also I'm in the process of ordering the STI Trojan in 40 s&w