For me it has to be Button, despite his dash/display issues.
I know he had a slow pit stop, but he should have never let Schumacher get by him into turn 1. His race was completely compromised from this point on as he couldn't find a way around him for the rest of the GP.
But it wasn't just the fact that he was stuck behind Michael, it was the utter lack of creativity in trying to find a way past. Jenson had at least 3 excellent opportunities to run one up the inside on him into turn 1, but again and again he opted to try the outside, where Michael easily held him off.
The onboard feed was with Schumacher when he got by Button, and then it switched to Button for at least 15-20 laps, giving us a great view of the Mercedes from behind.
If Button hadn't been stuck behind Schumacher, I believe he would have grabbed the third podium spot from Vettel. He only finished 12 seconds behind him, and I reckon the Mercedes held up Button's McLaren for much more time than that. Jenson should have been right there to pounce on Seb with his extra pit stop and brake issues.
I've posted the Schumacher - Button scrap here.
http://www.dailymotion.com/video/xd96w0_spa1001