There’s currently a debate of whether Biden is better off picking a Progressive as a VP or a woman or moderate Republican. Depending on your perspective, Elizabeth Warren is the safe bet because she would get the Progressive vote and be the first female VP.
From a debate standpoint, if she can tear into Pence like she did Bloomberg she would be a definite asset.
From a position standpoint, she seems to be more flexible in changing her platform and so is less likely to move Biden too far to the left and turn off Republican and Independent voters.
The Sanders camp is rumored to be against her nomination, however, it’s unclear how much power Sanders has at this point: he’s surrundered a huge chunk of his delegates by dropping out.
FWIW, I think Biden needs a female VP for damage control on all of the allegations by women that have been made against him—and that will be exploited by the Trump media campaign.
I think Hillary Clinton as VP would be the ballsiest pick by the Biden camp: they would get massive turnout on Election Day, however, it would be a massive gamble as far as which voters turned out more with HRC on the ballot.