If BA He-man had the spinning damage drum he'd be my choice in a landslide... but I have to vote Rattlor.
BA He-man leads with an axe swing that breaks Rattlor's staff in two. Rattlor trips BA He-man with a tail attack and kicks the axe to the side. They exchange blows. But BA He-man grabs the snake and punches him and begins to choke him out. Rattlor uses his rattle to cause BA He-man to lose focus for a moment and Rattlor is able to sink his fangs into BA He-man, biting through his magic armor and leaving him unconscious.
Rattlor narrowly defeats Bright Abs He-man. And slithers off to the next round.
Rattlor's MOTUC representation is epic, and when they add his General's armor he will be one of the best figures in MOTUC.