I entered LE in 1977 and chose to carry my personally owned 28 over the 15 I was offered. We were allowed to carry magnums, and I carried two of the new-fangled speed-loaders on my belt and two more in my unit. Over time, I experimented with other revolvers; 19's, 66's, etc. in various barrel lengths. However, having been raised in a military family, I was well indocrinated in the advantages of the 1911 and the .45 ACP. In 1982, I became the rangemaster, and lobbied heavily for the 1911. I eventually talked the Chief into the transition to autos, but only to double action platforms. Since I developed the program, I was given a lot of say in the structural requirements for the pistol. It had to be American made and steel-framed. The only two such pistols available at that time were the 645 and Colt Double-Eagle. As you might guess, the 645 won out.
Due to the magazine problems that S&W experienced during that time, we later transitioned to Glock 21's. In 1993, I changed to my hometown department, which was still carrying revolvers; 19's and 66's. Took a little getting used to, but eventually I stopped feeling underarmed (although I did carry a Sig P228 and extra mags in my car after being involved in an in-custody death incident that brought a lot of heat for a time).
Today, I carry my issued Glock G17 or G26, depending on my activities. I always carry G17 magazines when I carry the 26. Off-duty, however, it is common for me to carry a 940, 65, PC681, 4516, 4566 or one of my 1911's. The GDHP 124 +P ammo we are issued is what I carry in all of my 9mm guns. I have seen it's effectiveness and don't worry about it's potential for ending a problem. I always carry revolvers, primarilly .357 or .44 mag/special if in the mountains or desert. I always carry plenty of spare ammo, depending on the application, usually in speed loaders or moonclips (940).
The point is, as so many have said, shot placement is most critical. While I can shoot consistently high scores with all of my guns (because I shoot on my own time and dime ALOT), the world is an entirely different place when someone is shooting back at you. There is no such thing as having too many rounds.