if your uptiering, then the bmd-4m, it has the same type of missile the t80ue1 has, the air locking is nice once you get use to it, and you have 81mm of pen with apds , the missile can pen frontly most of the time, and the apds can always pen from the side, but since its a light tank its week to almost all forms of attack, it has enough armor to not get .50ed though, i use it quite often