Am I alone in noticing that a lot of former cops mention revolvers? Since most police officers carry an ankle gun, etc I don't think fire power is such a big issue. The revolver with the cylinder and barrel has a much longer sighting plane and in the panic of a gun fight I think a revolver is the better tool. I'd opt for a 6" barrel if it could be carried. Skeet Skelton talked about a 5" barrel (if such was available). A 4" barrel is a concession to "carry ability".
If you get shot and "limp wrist" a semi auto it may get a stove pipe jam. I think a revolver would be more dependable. You can also use a flat bullet that ought to hit harder. I'd go with the .357 Magnum even though I also like the 44 Magnum. I'd go with the K frame since it is lighter weight and easier to carry. The L frame is more noticeable.
I've had two home invasions- that isn't much real life experience but on the first one I had a long barrel revolver and faced two perps and on the second I had a mid-sized semi-auto and faced 5 perps. The revolver was more noticeable, the perps stopped dead in their tracks and gave up, with the semi-auto the perps didn't initially see that I was armed and came a few feet towards me.
As far as reliability- I'd put semi-autos and high quality (S & W) revolvers on an even scale even though the revolver has a few more parts and IMHO a Gvt 45 1911 is probably more reliable. In any even, if I was to issue arms to a police force, a S&W Model 19 with a 5" barrel with SWC type heavy loads plus a back up ankle gun if more fire power was needed. If any officer wanted the option of a longer barrel- I'd let them have it.