There was a poll a few weeks back that showed Michelle Obama being the most popular pick; take that with a grain of salt because we all know how biased and skewed those poll results are based on a number of factors which we can't know.
That said, I think she did a lot of great work as First Lady and I'd happily vote for her. I think she's got the potential to get people fired up and excited about the possibilities, much like Obama did, and everything else aside, that's what we really need - excitement, enthusiasm, and for people to want to get out there and vote. I think she could provide that moreso than anyone else on the list.
It makes me want to vote for her. It's a tough job, only a crazy person wants it. We should only give it to people who don't want it lol. Like her or Jon Stewart.