I think it's impossible to state which one is the "greatest" musically since everyone has different musical tastes but just based on it's influence on music globally, my pick would be JAZZ. Jazz, more than any other genre of music has the ability to adapt to and absorb any other form of music and create a whole new genre altogether. Just a list of forms globally that Jazz has influenced..



Soul,Rock, Funk, Bluegrass,Western Swing, Jamaican Ska, Trinidadian Calypso, Cuban Mambo-Afro Cuban Jazz, Brazilian Bossa Nova-Chora-Samba Jazz, Puerto Rican Salsa-Latin Boogalu, Nigerian Afrobeat, Ghanaian Highlife, British Skiffle, New Age Music, Ethiopian Jazz, North African Rai, Electronica, Haitian Zouk-Compa, Argentine Tango, South African Mbaqanga, Arab Jazz, Gypsy Jazz

Jazz's global influence is unmatched IMO.