It will probably be a Clinton/Warren ticket.
I guess it comes down to whether she can pull off the "working class" thing in Middle America or whether she's just going to be seen as another rich law professor. I'm thinking the latter.
Most likely Hillary would be stronger than Obama among the White working class and it's hard for me to see what votes Warren could snag for her that she wouldn't get on her own. IMO, a Latino or a middle class White guy could help her with Hispanic or White constituencies more than Warren would.