Wow, two legendary villains. The main reason I'd give it to Joker is that within their respective films, Joker gets significantly more time to be a villain than Scar, to the point that many people consider the Dark Knight to be the Joker movie since he gets so much focus. Scar is basically absent for the Lion King's entire second act. Don't get me wrong, Scar is awesome when he's on-screen, but we just go so much more time with the Joker.

Both, both is good

Joker. He’s more iconic, imo.

I'm gonna be honest with you guys and please don't kill me it's my opinions Scar isn't that great of a villain

Agreed