I have to say I think Elvis was the bigger icon. He came along before "
my time" (Jackson came along a little after "my time"), so neither of them meant a whole lot to me, personally. Both had a lot of music that had a good sound or rhythm or whatever. Both were "showy" (but then so was Liberace - another one-of-a-kind icon).
Elvis, though, ushered in rock and roll. Also, he was among the first (if not THE first) to incorporate so much of the blues/jazz/sound of African American musicians into his music, bringing that sound into more into the mainstream, popular, music. He was the first to cause so many parents to be "concerned" about the gyrations he did when performing. His romance and marriage to Priscilla captured people's imaginations. The fact that he entered military service was a big deal for a lot of people as well. His death, the whole "Graceland Thing", the stories about whether or not he's still alive, etc. In my memory, it seems he was a "first" for all of that kind of myth and weirdness.