Captain Shiver-me-Whiskers Thundertron is my favorite so far, but he's not on the list so I voted Breakdown.
This ^^^ 1,000X this. RiD Voyager Megatron is absolute shit with it's lack of paint apps and brown plastic. But, Darkness Megatron takes the same mold and makes it unbelieveably awesome. The Arms Microns he comes with (Gora II and Hades) are absolutely epic especially Hades in scythe mode. He is a MUST HAVE for any TF Prime or Megatron collector out there. Seriously, pics do not do Darkness Megatron justice.