(Transformers) Megatron: Bombarded mercilessly by a squadron of F-22s and human soldiers, tripped over hard by Optimus and losing his leg in the process, All-Spark pushed into Megatron's spark ending his life for two years. (Transformers: Revenge Of The Fallen) The Fallen: Face sliced through by Optimus's sword, fingers severed, speared through the throat by his own staff, face plate ripped off brutally, Optimus's fist jammed hard right through his body with The Fallen's spark in hand. (Transformers: Dark Of The Moon) Sentinel Prime: Shot in the back three times by Megatron's shotgun, pulled over and pushed to the ground with his sword going over the bridge and into the water below, face plate kicked off his head by Megatron's foot, crotch ripped out, (remainder of the attack unseen due to end of Sam's fight with Dylan and the destruction of the main control pillar), shot in the back and head by Optimus Prime following Megatron's anti-climatic death. Out of those three.... It's a strong tie between The Fallen and Sentinel Prime. Seems that the enemy Primes always take the worst damage.