Hey...great question....and one that's been hashed over endlessly by the military and literally hundreds of LE agencies.
I had a cpl tours in Vietnam as an Air Force pilot and carried an issue S&W M15 until I could get a 1911 from the Army; on my first tour, as a forward air controller flying L-19's from a dirt strip, I lived in a Special Forces camp just below the Cambodian border. I spent a hellofa lot of nights in slit trenches, listening to the VC attempting to worm their way through our wire.
For that kind of duty, let alone slogging through swamps or desert sands, I'd pick a gov't issue 1911 every time. Loose enough to ensure good reliability with hard ball rounds, and enough punch to do a number at 3 feet to 30 foot threats... and make it a .45... a 9mm is just not enough when you absolutely need it at bad breath distance...if the "small hands" crowd doesn't like it, spend some training dollars to teach them. A pistol is for close in work, where you aren't carrying a rifle, can't find a rifle, or the long gun won't fit....
For LE use, I have no problem with a revolver, but then I"ve never had to use one in an LE capacity. Slower to reload, but inherently simpler...a revolver has very good characteristics when the adrenalin is flowing. And if it's a Smith M15, tell them to get a pair of stocks on the dam thing that allow you to shoot it twice without losing control...a grip filler is a good idea, or better yet a pair of Pachmeyers.
For the two years I was in Vietnam, I was never out of reach of a good handgun. Shower points, the CO's damned briefings every other week, the PX...it was always on my hip or in a shoulder rig. And come to think of it, that's been my policy ever since where legal.
Best Regards, Rod