I like using a combination of logic and vibes when I used historical characters and the like. Logic is for example ‘If Nixon loses to Humphrey, then Reagan would be the most likely candidate for the Alt 72’ as it were, as there’s plenty of evidence
Vibes is a bit more esoteric, but it’s when you pick someone who fits the vibe of the piece & period and is less evidence based over whether it works in a logical fashion. This is because sometimes, logic can lead to really boring ideas (the ones where the changes are so dull and minor that it boggles why would make it into a timeline) and so sometimes, vibes helps pave over what could be a dull piece.
That’s when hipster PM and Presidents come I think.
Additionally sometimes as in otl the boring, logical option doesn’t always occur and instead the one of vibes wins out etc.