Final answer:
The art of improvisation is the aspect of Dixieland jazz that is still an important part of modern jazz, shaped by artists like Louis Armstrong during the Harlem Renaissance.
Step-by-step explanation:
The aspect of Dixieland jazz that remains an important part of jazz music today is a. The art of improvisation. Improvisation is a cornerstone of jazz music, allowing musicians to express their individuality and respond to each other in the moment, creating a dynamic and interactive musical conversation. This was exemplified by the influential Louis Armstrong, whose improvisational skills earned him the title of "the most important improviser" in jazz history. His legacy, along with those of other great Harlem Renaissance musicians, continues to shape jazz music.