Consider this quote about early designs for the Saturn upper stages:
Formalized as Advanced Research Projects Agency (ARPA) on February 7, 1958, the group examined the DoD launcher requirements and compared the various approaches that were currently available. [...] They had already accepted Krafft Ehricke's arguments that hydrogen was the only practical fuel for upper stages, and started the Centaur project based on the strength of these arguments.
Was Krafft Ehricke correct: Is hydrogen the only practical fuel for upper stages? I mean in general, not just the Saturn or Centaur rockets. If upper stage design would be different for 1950s technology versus modern technology, please state which context applies to your answer.
Related, unanswered: Advantages of a Solid Fueled Upper Stage