I thought it was Aron, too, until I went to verify before posting. I didn’t bookmark the site, but one stated pretty definitely that Elvis himself preferred Aron. The story told is that the family spelled it that way to match Jesse Garon Presley, his stillborn identical twin brother.
I really thought it was spelled Aron on his gravestone at Graceland, but I was wrong – it’s Aaron there. It is Aron on his birth certificate.