TOPIC: Criterion for equations for Estimate At Completion (EAC) ?

I have seen the following equations for EAC

EAC = BAC / CPI

EAC = AC + (BAC - EV)

EAC = AC + ((BAC - EV) / (CPI x SPI))

Can you please clarify the criterion by which one of these can be used? Like, at which situation, should we use one particular formula from these?

EAC = BAC / CPI
Use this when you have a trend on your project you expect to continue, and does not pose issue to the project.

EAC = AC + (BAC - EV)
Use this if you had a deviation on your project, but going forward you expect the project to be brought back in alignment with plan.

EAC = AC + ((BAC - EV) / (CPI x SPI))
Use this if schedule performance must be considered (e.g. if project is behind schedule).

Thank you.

Which one to use, if the CPI or SPI kept changing at random till now? Is BAC/CPI the most commonly used?