I still think "We should wait and see," but of all of the leading names out there I like Kamala Harris the most for the likely favorites. She's eminently qualified, she's not from the same region of the country as Biden, she has cross-over into different constituencies, she's got the right balance of age and qualifications young but experienced in multiple levels of government, she's also not an old white man which is kinda vain but I think it's important when building a cohesive government leadership team, and politically, she'd be an asset in debates and being an attack dog for the president. From just a personal reason, I'd love to see a black woman be VP, if not president. I think she'd be a really good vice president and if Biden wins the primary, wins in 2020, then it sets her up to run in 2024 should Biden only be up for a single term.
I love Elizabeth Warren too, I don't know if she'd be a top qualifier because I don't know if she'd want to be second-fiddle to a candidate who very recently out lasted her as one of the final top candidates. This is why I'm still in "Wait and See" mode. If Biden continues to roll primary after primary and continues to build a runaway lead, she'd likely endorse him, and then when they stand together she could seem like a clear candidate for VP. But I don't think that'd come for a few months, and there will be a lot of hurt feelings in Sanders camp should she endorse Biden now while the race is still technically not decided. If... come late April when it's all but a formality that Biden is the nominee, if she endorses him then, those hurt feelings won't be as strong. She'd be amazing in debates, but I think we sometimes give too much credit to debates. Clinton wrecked Trump in 3 straight debates, but lost the general election. Warren was the best debater in the last Democratic debate, and she's out. Harris was great too and she's out. One time debate performances really don't make much of an impact on the election, though you'd still love to see Warren wreck Mike Pence.
Anecdotally, as a Massachusetts voter who was mostly in Warren's camp throughout this primary, I've heard from about 6 friends in the same boat as me that were very positive on Kamala HArris when she endorsed Biden, all basically having the same reaction "if biden wins, I'd love her as a VP pick..." It's just an anecdote but it's one I've seen repeated in person like a half dozen times enough to make an impression worth repeating.
I'm cool with Stacey Abrams but I don't think her political celebrity is high enough to be a serious choice. I think Abrams is in a similar position as Obama in 2004 where she can give a stirring speech at the Democratic National Convention, which can propel her into political stardom for 2024, 2028 and beyond. Unfortunately she's hamstrung in state wide races in Georgia, and so that national political fame will come at a political cost locally.