OOH, hard question as there are so many categories :!:
1. Pistol - Glock 21 or a CZ75. Both very nice weapons, especially for service weapons and I had some the best shot groups ever with both of them.
2. Submachine gun - M3A1. Can't beat the old grease gun for shear slamming .45 cal fun (the last time I fried one, I had some pretty good 3-4 round shot groups at 25 and 30 meters).
3. Rifle - M16A1 (most familiar with this one). Maybe not the bestr wervice weapon anyone ever came up with, but good to go.
4. Machine Gun - M2HB. Nothing beats the old .50 cal for sustained firepower, noise and punch. You have to love the way the tracers arc away after hitting (and going thru) the target.
5. Larger calibers - M109 (any model) 155mm howitzer or the M110A2 203mm howitzer - especially at Charges 8, 8 Super or 9. Have to love the noise and blast.
I'd rather be a Soldier with a mule and mountain gun, than Knight of old, with spurs of gold, or Roman, Greek or Hun. For when there's trouble brewing, they always send for me!
Mortui Non Mordent - Celeritas Et Accuratio