What pilot was the top American ace during World War 1?

Edward Vernon Rickenbacker. Rickenbacker was at the time said to be credited with 26 victories, but today is often said to have 28.

Frank Luke was second with 21, all destroyed in seventeen blazing days of combat before he was killed. Luke was the only American airman awarded the Medal of Honor while the war was still going on. Rickenbacker was awarded the MOH in 1927.