Clark/Biden, maybe - Clark has executive experience, while Biden has legislative experience. Maybe Kerry, HRC, or Kennedy
Biden--Good candidate on paper, but makes a lot of gaffes and that could hurt the ticket.
Kerry--Good pick.
Hillary Clinton--It might have helped with women. However, it might have hurt because Hillary would have been very polarizing, perceived as kinda inexperienced, and because it would be kinda awkward to pick a former First Lady as VP.
Ted Kennedy--No way. Bad pick. He was too old, too liberal, and Chapaquiddick would come back to haunt the ticket and Clark's judgment in picking Kennedy.