I almost hate to admit it, but of Mitt, Ann, Paul, Barack, Michelle, Joe...
Michelle is arguably the best orator of the 6 of them. She can actually speak with a balance of seriousness (which Biden lacks, for example), and a connectedness to her audience (which Romney lacks).
That's because her audience is full of fembots, the same droids that chanted Yes We Can until their mind turned to pudding