Mattis should be the first call for VP. Kelly should be second.
In no particular order, my short list
Whitmer (strong gov, intelligent charisma)
Shapiro (")
Newsom (points for visibility, but maybe an all-Cali ticket a bit much for middle America)
Buttigieg (for maximum Firsts per ticket)
Mattis (an honorable man in any universe)
Cheney (Unity tickets don't often win, but LIzzie could swing some Lincoln Project folk and other defectors)
Booker (this guy is fucking serious about affordable housing and has terrific energy)
Beshear (so I can keep making a terrible pun, as witnessed here earlier)
Cali electors could not vote for both Harris and Newsom under the 12th Amendment. Besides, he has horrible taste in first wives.
Who most helps the ticket get elected? Of the ones you mention, i think Shapiro does the most. Kelly .akes some sense, though he has lite experience, perhaps less of an issue up against a DEI pick like Vance,, and his advantage is being a border hawk, if Harris wants to slide away from the Biden record.
And the Veep does need, generally, to support the policies of the President. Cheney would not do that, and Mattis... supposedly has no politics.