I still haven't seen any significant revelations come out of wikileaks, so I think they were right to not pick Assange
If there's no Facebook I honestly don't think the world changes all that much. People are on MySpace, and some of the other social networks are more popular. 10 years down the line, I don't think the world looks noticeably different. Whereas I think with Wikileaks the whole dynamics of US foreign relations will change.
Both are speculative, but I do think that Wikileaks is more impactful than Facebook. With that said,if they gave the award to "the social network", I'd be in more agreement.