Normally I would say Wh40K for this, but there is one pressing concern: EVERYONE IN THIS UNIVERSE IS A HERETIC TO THEM.
They will kill all the aliens (most of who I like) and then enslave us. That's just the Imperium, and it gets worse from there.
No, I have a better idea:
BolosBasically, in the later marks, giant, self-aware, tanks that are loaded with shielding and firepower enough to give the Reapers a big one finger salute. Even "malfunctioning" units can still remember who NOT to shoot and beat the ever loving crap out of the enemy.