I think NERVA and its Soviet equivalent RD-0410 were much more practical and plausible. Unlike Orion which was complete vaporware, both these projects reached the ground test prototype stage.

https://en.wikipedia.org/wiki/NERVA

https://en.wikipedia.org/wiki/RD-0410

NERVA / RD-0410 are basically like chemical rockets but better (maybe 800s specific impulse, vs. 300 for a chemical rocket). In contrast, Orion was 6,000s to maybe 100,000 theoretically.