One trait that Leo and Stargirl both share is their confidence in their unique individuality. Granted, Stargirl is way more comfortable and confident in being her own person than Leo is. He is still much more affected by peer pressure, but readers do get to see how Leo has confidence in himself liking things that are considered weird or not trendy. For example, he likes porcupine ties:
When I was little, my uncle Pete had a necktie with a porcupine painted on it. I thought that necktie was just about the neatest thing in the world. . . . I loved that porcupine tie so much that I decided to start a collection.
Both Leo and Stargirl are capable of loving people by accepting the other person's actions or personality. Again, Stargirl is better at this than Leo. It's why she is able to kiss Hillari after being slapped. Leo shows his ability to love people regardless of their quirkiness by being friends with Stargirl and Archie. Archie is basically the neighborhood goof, but that doesn't stop Leo from talking to him and seeking his advice. The love of people and goodness that Leo and Stargirl share is also demonstrated in their missions of random acts of kindness.