Well one thing we do know is that selecting a female running mate will be a strategically smart decision. Picking Mitt Romney will be a Biden-like mistake. Even worse maybe.
You never pick a VP with baggage. Evidence of that goes back a long way and in modern times one can start with Tom Eagleton in 1972 for the track record of presidential candidates who pick VP candidates with baggage.
Musing about Sen. Tom Eagleton for a moment, it probably hurt McGovern more in unceremoniously tossing Eagleton like a hot potato rather than standing by him (especially if the psych gave Eagleton a clean bill of health).