Sorry for the rather predictable answer, but I choose the gun HE/HEAT/AP depending on the situation climate and whether or not I have a known gunner.
AP Titan because if I want HE Ill just pull a Lightning. Vanguard is for serious AT duty, not for Infantry farming.
I almost always Roll AP main, and ML85 secondary. 9/10 i will see armor, or make it a mission to take out an enemy sunderer. I can snipe infantry pretty consistently with the AP gun, and my gunner usually does alright as well. The only time Ill roll HEAT is if there is just an absolute mass of infantry, and I cannot see myself ever needing the AP gun. I have maxed out zoom and ammo for both guns. Maxed reload for my AP gun. Max shield, racer chasis, and front armor.
AP or HEAT depending on how big the balance of the expected battle is between enemy armor/infantry. For general cruising around though I always go with AP, because I would rather be able to wreck enemy vehicles, and can simply drive off if the infantryside is too intense for AP/Enforcer AV.
