That is a good question. In the movie, I felt that Optimus was more civil and reformed than Megatron, who in turn was much more animalistic and primal than Optimus. Optimus was probably thinking about the Allspark and Sam's protection, while Megatron just cared about beating the life out of Optimus. It was definetely one-sided, but I think with good reason. Perhaps in the sequel we will see a re-match?
I'm glad it was more one-sided, just for the reason that Optimus Prime is civil and just plainly a nice guy...yah, he killed Bonecrusher with ease, because that was just a soldier, but Megatron is a huge threat, and even if Prime saw that he killed Jazz, that still wouldn't show Prime beating the crap out of Megatron.
That's why he said he'll destory the All Spark using his Spark/Matrix of Leadership, because he probably knew that if Megatron returns, he had to destroy the All Spark because he couldn't beat Megatron.
I don't want a rematch though...the final battle in Transformers between the two was amazing, but for a better match, I'd like to see Optimus Prime vs. Starscream.
And I have a great idea for that; Starscream returns, finds Energon in underneath the Earth's crust below oil fields or in the ocean where Magatron was dumped, and ala Beast Wars, it gives him more power like Terrosaur, and also makes him bigger, which changes his jet form into a bigger, and possibly a blue/red/white jet like G1, and those two go at it.
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