Biden has painted himself into a corner, and I think he has to pick an African American woman.
His best choices by far would be Oprah Winfrey or Michelle Obama.
Neither has any experience in elected office, but Trump himself has killed any and all fear of that being an issue. I believe the problem with Oprah is she would never accept second chair to anyone. She is also a mega-billionaire, and Progressives don't trust capitalist billionaires. Plus, because she's a mega-billionaire... and she's much more of a billionaire than Trump will ever be... she won't release her tax returns. This would severely handicap a strong Democrat talking point against Trump. If she tries to release something you can take it to the bank that's it's not the real deal, and Trump will immediately know where to look to exploit the false documents. So, no on Oprah.
I don't think for a second that Michelle Obama wants to leave her current wonderful life for the very tall order of debating Mike Pence and attempting to save Joe Biden. I don't think she likes Joe Biden enough to risk the attention. Michelle is a no.
Susan Rice has the gravitas, the charisma, and the political chops for the job... but she has always been a behind the curtain player, so she has a name recognition issue. She carries a lot of baggage from her years in the Obama Administration, and may earn herself a little problem that goes by the name of U.S. Attorney John Durham. Susan is a possible.
Kamala Harris is a Californian with a well known reputation of sleeping her way to the top. She is never seen as a very serious politician, but she could supply Joe with some much needed populism... but she's still from California, and Biden needs no help winning that monster state and taking all those electors. Kamala is possible... but Rice is a better choice.
Stacey Abrams is just a loser all around. Joe needs to stay away from the southern states at all cost. It's a no on Stacey.
What Joe really needs he can't have. If I was Joe Biden running against the human juggernaut known as Donald Trump, I would do everything I could to get a populist name on my ticket. The choice would be Alexandria Ocasio-Cortez. She's a goddess to Progressives... but she is also far too young to run on the ticket.
No matter what... the song remains the same, and Joe Biden's worst enemy is Joe Biden. Hillary Clinton was a much stronger candidate than Joe Biden, and she lost to Donald Trump. Donald Trump is a much stronger candidate now than he was in 2016 when he won the election against Hillary Clinton. So, it's not likely that Joe can beat Donald. This is of course my opinion... I could be wrong.