My armor setup looks like this:
LARM-LARM-AC => Early war CA armoured division.
LARM-MECH-MECH => A fast spearhead brigade. High firepower and spe, but only decent softness.
ARM-ARM-MECH => Lower softness and more hard attack, but slower. Better if the enemy has tanks on his side.
HARM-HARM-HARM => Does not use the CA bonus, but is very effective thanks to low softness, esp. vs units lacking proper HA (basicly anything but AT, TD and other ARM/HARM)
LARM-LARM-AC => Early war CA armoured division.
LARM-MECH-MECH => A fast spearhead brigade. High firepower and spe, but only decent softness.
ARM-ARM-MECH => Lower softness and more hard attack, but slower. Better if the enemy has tanks on his side.
HARM-HARM-HARM => Does not use the CA bonus, but is very effective thanks to low softness, esp. vs units lacking proper HA (basicly anything but AT, TD and other ARM/HARM)