AO 2012 by far.. Everyone expected a competitive match at least, but it ended up being an embrassing beatdown!
As far as the Olympics final is concerned, the winner of that tournament was a sure thing since the beginning. Nobody expected Maria to even win a set! Serena is one of the GOATs and she was playing her best tennis on her favorite surface. No shame in losing to that kind of player. Moreover, she nearly lost to Lisicki, so the silver medal was an incredible achievement.