It depends on which version of the game you're talking about.
Stock: Popups and rammers are the way to go my friend.
DSL: Use a Dual Perm/MOE motor/6 mag gearbox and have a tribar/disc/DSLbar with hammers on it and it should deliver an average 1500-2000 hitpoints per hit, i've had a bot reach 20,000 hit points on the first hit before.