[brudgers]

What will users get out of logging in?

Which is to say that the first options would be simply for the app to work without anyone having to log in. That's practical for some apps, and of course not for others. The larger point is that just as a login mechanism might not be necessary, if it is necessary the choice of mechanism should make sense given the nature of the app...don't use Twitter for a self-help app for narcissism or Instagram for a seniors lifestyle app.

As for the alternatives, what good could possibly come out of storing name/email and password pairs?