Voyager class Megatron looks a bit more faithful to the movie version, but the trade off is that he's covered in clear plastic ice, and that he's slightly shorter than Voyager Optimus Prime, when he should be slightly taller to be film accurate. He still looks like a great figure though, if you don't mind the ice motif.
I'm planning to get both Optimus Prime and Megatron in voyager class, because I think that they look overall sleeker than the Leader class ones, and they are much cheaper - $20 versus $40. The only problem is that we'll probably have to wait another week or two before they're available in stores.