On SI-SOY: assuming "already having won" is a factor — and I suspect it's a huge one, since the only multiple winner in the 60+ year history of the award is Tiger Woods — that eliminates LeBron (2012) and Phelps (2008), and at least partially eliminates Ortiz, who earned 1/25th of the 2004 award.
Maybe I'm biased by having watched more track and field than gymnastics this summer, but I kinda feel like it should be Bolt ... no? Greatest sprinter ever, totally beloved and venerated worldwide, has never won the award, and this is their last chance to give it him. I'm sure Murrica is a factor, but it didn't prevent them from selecting Bobby Orr in '70, Gretzky in '82, Johann Olav Koss in '94, or Sosa in '98.
Anyway, I vote Bolt.