I would say Gephardt. Though I like Edwards, and think the Democrats could have won with Edwards as their Candidate, Gephardt fits better with Kerry's theme. It's a dangerous move though, since Gephardt has a lot of baggage with him, and may not necessarily deliver a state. They would have to campaign on "experience" than anything else.
Well either Gephardt or Edwards would help shore up Kerry's protectionist credentials, but Edwards personally fits better with Kerry to balance out young and old, whereas Gephardt just comes from a very strategic areas. One thing though, is hopefully whomever the VP is does not constantly point his or her finger or lift his or her hand during debates and speeches. When Kerry does that it is like he is lecturing and is seriously unattractive. I know he knows more about the issues than me but would like to see his face unhindered by his hands.
