There's a lot of talk that Barack needs to choose a traditional "white male" for VP. I'm not sure why. I guess some people think the Democrats need to "balance out" their black, femaleness. Whatever. The sociological politics of this race are a minefield and I'm sick of thinking about it right now.
But if it's decided that they need to go this way, then Clark would be my choice over the others who are most often discussed. (For many different reasons, some of which are well articulated here, by Kathy G.) He's proven himself to be a true blue progressive, tough as nails and selfless in helping fellow Democrats get elected. He's also very smart, has about the best military resume for leadership you can think of, and he's from Arkansas. He makes it very difficult for the Republicans to claim that the Democratic party doesn't understand the military or foreign policy.
I'm agnostic on the VP choice. There are good reasons to pick a number of different people, including Clinton. The campaign will have to analyze their strengths and weaknesses and see what the landscape looks like when the time comes. But if they decide they need a guy whose worn some salad on his chest, this is the one, IMO.