I'd go with a Glock 20.
The two biggest cons that would make it difficult for the gun to pass government bureaucracy are the grip size and lack of external safety. As someone on this thread has already pointed out, Glock would probably be quite happy to add some external safety for a contract of this size. As for the grip size: 1) It takes practice and training, but it is manageable -- I've got modest to medium sized hands for a guy and shoot mine comfortably. 2) Glock's backstrap is large and not necessarily necessary (although it does contribute to the Glock signature grip angle). For a large contract Glock could eliminate this. I've seen & held a G20 with a grip reduction, and its not too large at all.
Other cons:
Due to powerful recoil, there is an increased likelyhood of a round failing to eject cleanly if the shooter limp wrists it.
(This can and should be overcome by training, and is very fast to clear).
Pros:
Light weight
Comes from the factory with accessory rail
Very corrosion resistant
Bigger hole than a 9MM
Reliable in harsh conditions
Simple and instinctive to use
Big, fat sights make aiming easier at longer range
15rd capacity: not bad overall, better than any .45
Good penetration of urban obstacles like wooden fences, glass, car doors, some building material (this could be a pro or con)
Extras for each service:
All reserves:
>60% of police departments either issue or allow officers to choose Glock. Glocks are also common civilian weapons. This improves commonality with war fighter's civilian weapon.
Air Force:
10MM is a great hunting round, add detachable stock & you have a survival rifle.
Special Forces:
Lots of power, used with choice ammo, it can penetrate light armor that might be bought be drug lord lieutenants at military surplus & other venues. Or with armor penetrating ammo or special upgrades like 9X25 Dillon extended barrels it may have some capacity to defeat modern soft armor.
Army/Marines:
A bit lighter than all metal guns of comparable size, power, and capacity.