Blackout FTW! His design is awesome, he wrecked everyone in his path and he kills you with rotors and scorpions. Rock on, Blackout.
All Baycons have great design, but I dont recognize characters, so I say "No ONE". They die like cowards, because screenwritters havent feel for villains.
I say Starscream. I like that Decepticon usurper and I love how he was depicted as a badass leader in Reign of Starscream.