In terms in insane genius and magnificent sarcasm, BW Megatron is tough to beat; "When expecting a bobby trap, always send a boob in first"
Transformers Animated isn't as witty, but IS a Magnificent Bastard, with his wonderful approach to dealing with the treachery of Starscream. As opposed to G1's Megatron "I shall keep him around.. just in case the plot requires that he betray me again", TA Megatron's response was to blow his head off IMMEDIATELY he had a chance... and when that didn't kill him... he shot him again... and then had a standing order for all Decepticons to shoot him on sight. It was incredibly refreshing.