if we're talking ANY gun then
if they're demilitarized i'd get this because war history-
T8 105mm AT gun
was mounted on some T-32s and was going to be mounted on the experimental T-29
if they're NOT demilitarized i'd get this because loving amazingness-
M256 120mm AT gun
rheinmetall really outdid themselves with this beauty. interestingly enough it went back to the concept of smoothbore because rifling is pointless for APFSDS/sabot/hvap/apcr/same stuff different name shells when they already have fins... in fact, it tends to decrease the accuracy on a finned projectile.
the main reason that, say, britain, still uses a rifled tank gun in the chally 2 is because they rely on HESH, which NEEDS to be spinning in order to properly impact a target.
but if we have to be boring and get a small arms weapon i'd go with one of these beauties
top: SCAR-L, bottom: SCAR-H
to quote wikipedia,
"The Special Operations Forces Combat Assault Rifle (SCAR) is a modular rifle made by FN Herstal (FNH) for the United States Special Operations Command (SOCOM) to satisfy the requirements of the SCAR competition. This family of rifles consist of two main types. The SCAR-L, for "light", is chambered in the 5.56×45mm NATO cartridge and the SCAR-H, for "heavy", fires 7.62x51mm NATO. Both are available in Long Barrel and Close Quarters Combat variants.
The FN SCAR systems completed low rate initial production testing in June 2007. After some delays, the first rifles began being issued to operational units in April 2009, and a battalion of the US 75th Ranger Regiment was the first large unit deployed into combat with 600 of the rifles in 2009. The US Special Operations Command has currently cancelled their purchase of the Mark 16 (or MK 16) SCAR-L and are planning to remove the rifle from their inventory by 2013. However, they will purchase the Mk 17 SCAR-H version, and also plan to purchase 5.56 mm conversion kits for the Mk 17, supplanting the loss of the Mk 16. The SCAR was one of the competing weapons in the Individual Carbine competition which aimed to find a replacement for the M4 Carbine."
