1] Obama picks a woman who's approximately as Lefty and as feckless as he is. McCain picks a woman, too. He's got much better choices than Obama does.
Obama gets no bump because his choice is somebody like Feinstein, Boxer, or Albright. McCain gets at least a few votes from feminists who think he looks like he's going to die soon
Obama defuses some of the reaction from the women disappointed by Hillary's loss, but he loses the general election, because of his lack of experience, absence of American identity, and shaky foreign policy creds. His Feinstein/Boxer/Albright running mate doesn't help.
2] Obama picks a man who used to be a General or something. McCain picks a woman.
Obama's Lefty General helps fill in some of Obama's missing resume, but the ladies freak out and turn the convention into a circus, make the Dems look like fools, and either wrangle the nomination for Hillary or make Obama grovel like dog.
McCain gets lots of votes from feminists who think he looks like he's going to die soon.
Obama goes down hard in November.
3] Obama picks the General and McCain picks a young guy who looks like he could take over if need be and who's from a swing state. The ladies freak out at the Dem convention and sit out the general election. Obama increasingly looks like the fool he is and can't close the deal without the feminists who are home dreaming of 2012.
4] Obama picks a woman; McCain picks a man. Obama gets through the convention OK, doesn't get any benefit in the general from his VP choice but thanks his stars McCain picked a man. Obama has his best chance in the general.