I don't think I can recall a single more important VP selection than Biden's VP selection.
I think Biden will win, based simply on the fact that Trump is so disliked. If you asked me in early January if I'd vote for Trump against Sanders (the presumed nominee), I'd probably say Trump. You ask me that question today, and I would vote for my cat over Trump - and my cat is dead. His response to COVID-19 has been an absolute disaster, and we're just starting to feel the real economic pain. By November? Good lord it'll get ugly.
Biden is leading all over the map based solely on the fact that he's not Trump. He needs some young energy - obviously. If his VP pick is a female (which he said it would be) and a female of color (quite possible - Harris most likely) than I don't think Trump can beat him. At this point, he's hardly campaigning, as it's more advantageous for his campaign to just let Trump continue to self destruct. I'm personally stunned at how inept Trump has been over the past 3 months... just 1000% reinforced every bad aspect about him.