As I have stated before I would prefer, for the size and weight, to carry an extra fully loaded rifle magazine and/or a hand grenade or two and skip the pistol.
That being said if I was going back into combat and had to carry a handgun, I would pick the Glock. If you have ever lived out of a rucksack, with everything food, water, shelter, defense being carried in a pack on your back, you want to shave every ounce that you can....the last time I did a comparison the Glock while not the best at anything was the best compromise and the lightest still reliable still combat accurate high capacity handgun made.
The Military does not like it because it has no safety,,,I see that as a huge advantage as no handgun should be carried without a holster that completely protects the trigger guard and if I draw the handgun I intend to use it and the safety is just something to get in the way and take precious time even if it is just a split second, also something to potentially forget in the stress of potential death.
Remember Mil-Spec,,,is not always the best but the best the Military is willing to pay for that gets the job done,,,if you have the time to do the research and the extra money to spend you can in many cases find better than Mil-Spec but as the other posters have noted,,,it probably makes no sense economically or politically to replace the Beretta at this time except for special missions requiring a special handgun somewhat better for the job.
Life Member,,,Military Order of the Purple Heart, Veterans of Foreign Wars, American Legion, Amvets, Disabled American Veterans, 173rd Airborne Skysoldier Association, National Rifle Association, Member,,,IDPA, USPSA, Iowa Sheriffs and Deputies Association,,Website http://www.handgunholsters.net