But to answer your question this is a hard one. And I'm personally glad you asked this question because people for sure like to look over the fact the Scorpio's have MASSIVE ego's themselves. It's just that Leo's are such an exuberant and vital sign which is why you don't notice it as much with Scorpios. Leo's are ruled by the Sun and the sun brings vitality and gives life which is why Leo's tend to get the most attention and rep in the egotistical department.
I honestly can't pick because some Leo's are more egotistical than Scorpio's and some Scorpio's are more egotistical than Leo's. So I'll just say this. At the end of the day Leo's are"commonly" much more renowned for being MUCH more warm hearted and loving than Scorpio's so I think Leo's positive traits out shine the who "Leo's are so egotistical" thing.
If you notice, (and astrology has said this about Leo's as well), when a Leo is happy mostly everyone will usually be happy due to Leo's being a source of life and energy and wanting to help others...When Scorpio's are happy, it's usually only that Scorpio that is happy because Scorpio's are only 100% at ease when in their eyes are in total control over everything and everyone ans using others. Not helping then.
Sure both Leo's and Scorpio's are the powerhouses of astrology with huge ego's, but ask yourself on a general bases who makes up for it will a forgiving, loving and deep down genuine nature that only wants to see people happy? Ask your self when one of the two signs egos are not fed, who resorts to violence, grudge holding and vindictiveness as a means to get rid of the perceived threat?