Obviously, Scar would be my primary choice. Cause he is the "real" villain of TLK and he had his moments. Like that part where he says: "I'm surrounded by idiots". He was also clever to successfully plan out his secret killing of Mufasa .
Since you got 2 selections, I also chose Shenzi as well. Between her, Banzai, and Ed, if there's a leader here, it'd have to be Shenzi. She kicked butt and stood up to Scar telling him that the Pride Land's natural resources were gone, even though he denied it. Whoopi's voice was perfect for this character. And oh yeah.., I laughed hard at that scene where she tells Banzai: "There ain't no way I'm going in there! What, you want me to come out there looking like you? Cactus-Butt!?"