I am a fan of Glocks but also have a soft spot for Sigs and 1911's
After carrying the Sig Mk25 and a Beretta on deployments and my Glock 19 Gen3&4 at home here is my uneducated knuckle dragging non operator opinion.
If I wanted a full size open carry duty gun and I was not worried about $ I would probably choose the Sig 226 9mm, it's a sweet shooter and well suited for open duty carry for a police officer, armed guard etc.
If I was on a budget or needed a dual role pistol (duty/open carry and concealed carry) and could only afford or could have one gun I would choose the Glock 19 Gen 3.
Beretta 92 Full size are good duty pistols and durable but the slide mounted safety always annoyed me.
I don't have enough time behind a 1911 to make a determination on that one, although if I was in a state that restricted magazine capacity I would probably learn to master it and I would probably buy a commander size aluminum frame.
If I was king of the military I would just go Glock 19 Gen 4 with night sites because of the cost vs. use/durability.
1. You just can't beat Glock durability, cost, easy maintenance, and availability of accessories and holsters. Its a simple manual of arms and they cost less than others.
2. The Gen 4 has a bigger magazine release and comes with back straps so each user could in theory when its issued to them find the sweet spot back strap for them (I know these would end up in a bin in the armory but the option would be there). Will fit probably 95% of regular people in the armed forces.
3. The frames would outlast the Sigs (nominal of about 25k down the pipe before frame cracks around the magazine release) and the cost is below both the Sig and the Beretta.
4. They would be outfitted with the NY1 spring and - connector just to minimize (the almost non issue of spring breaks) and keep a nice DA type pull.
5. Second strike capability is nothing to worry about since everyone is taught tap, rack bang for the most part.
6. Weight is down, the damn thing doesn't weigh anything.
7. Most of the time unless you are military police or security forces on a non war zone installation, for the most part the pistol is a secondary weapon.
8. If people wanted to have extra magazines(and their unit allows it) it won't cost them an arm and leg to get some.
9. Lots of MOLLE pistol pouches will take Glock magazines just fine so your good there, the holsters are a drop in the bucket when you do bulk purchases from safariland and blackhawk.
There are so many upsides to a Glock 19 Gen 4, I logically can't think of a reason the US armed forces shouldn't replace all other pistols outside of special roles such as dog training(revolvers), suppressed use (Hk 45c) etc with a Glock 19 Gen 4 as described above thru attrition of the M9 and Sig Sauers in inventory.