Ok since having weapons over here are a no no, i dont know much about them. However i did spend 6 years in the armed forces so i can only go by the weapons ive used. They were GPMG 7.62, SA80 5.56, BROWNING PISTOL 9, LAW 80, MILAN, and a 66. Since the last 3 are for taking out tanks, light armor and bunkers it wont be one of them.
I would have to settle for the SA80, its light and reliable. The magazine holds 30 rounds which are 5.56mm so there small enough to carry shit loads. You can fire single shot or have it auto, the sights are SUSAT, which make them hard to miss your target. The only down side is the round is relatively small so to kill someone it would have to be a head or heart shot. This said if i could have a Warrior tank then that would be my choice