i voted elvis but i think he only barely edges out Sinatra, Sinatra probably had the best voice of all time, but without Elvis rock music would barely even exist today.
the beatles are definitely icons, and i think lennon is iconic himself, but not to the extent of elvis, i think without his influence music today would definitely suffer, but there were great bands similar to the beatles at the time the beatles had gotten big, so i think rock music would have still pulled through
tbh i like Michael Jacksons music, but i think his biggest contribution to music has been dance, he revolutionized dance, he's now the benchmark for amazing dancing. the dance style popularly associated with rap music (even though hip-hop is completely different from MJ's style), would not exist were it not for jackson, so we definitely can't sell his influence short.