Let's face it, Buffy is to selfish to be the best leader. She always did manage to pull through, and her particular point of view has kept her alive, but she did a lot of stupid things, got a lot of people hurt and killed, aka Xander, Kendra, Willow, Faith, gosh almost everyone has suffered at one point from her selfishness. Wether it be in forms of neglect or bad decisions that lead to violence, everyone was affected. Buffy did some amazing things, scarified so much for the world, but really she was not that great of a leader, but that's why we lover her. like us, she's not perfect.
BUT.. Angel is not that much better, lol.. He can be really self-centered as well. Overall he seems to be more stable as a leader, though not by much.