Personal opinion is Quan is stronger but Shang is more skilled and a better hand to hand fighter.
has anyone considered that Quan chi being stronger is all the amulet's doing? In MKSM before he had the amluet he had none of the moves we know him for from MK4.
Shang Tsung is the book smart kid who gets straight a's in school and can probably lecture to his teachers, but that's all he is. Nobody likes him, nobody listens to him, because they know he can't do much else besides solve every single equation thrown at him. Quan Chi is the clever kid who can manipulate/beat up everybody into doing what he wants. He's not an idiot, he's smart enough to know how to manipulate people and beat them up, and probably even does pretty well in school on his own. He's not as smart as the other kid, but he's a lot more feared and respected.
It's true, nobody respects Shang Tsung. Shao Kahn treats him like a toe rag, he's always getting beat by Liu Kang, and the only major accomplishment he has to his name is winning the Mortal Kombat tournament before Liu Kang got in the fray.
As opposed to Quan Chi who has his own league of netherworld assassins, an amulet which grants him immense power, and a place at the side of the most powerful enemy in the MK franchise, Shinnok. But wait! All those qualities are stolen, borrowed, and riding entirely on his remaining affiliated with other parties. Quan Chi has not done ONE THING on his own in the entire MK franchise. So yea, I'd say the manipulative bully persona fits him. But deep down, aren't all bullies kinda pathetic? After all, it's the nerds that get to be CEO later in life.