I worked this table out with ChatGPT (with all the caveats that implies):
https://gridwhale.com/program.hexm?id=GCJ5TL7Z&file=GCJ5TL7Z...
Basically, nothing short of antimatter rockets will get you a self-contained interstellar ship.
Ion propulsion, even with nuclear reactors, can't get you enough speed.
Fission-fragment reactors can get you up to 1% lightspeed, but that's still 400 years to Alpha Centauri--I'm not sure I would trust a generation ship to last that long. Advanced fusion might cut that down to 100 years. Antimatter can reach 20% lightspeed, which means 20 years to Alpha Centauri.
ChatGPT kept asking to design a laser sail (external power source) to avoid the tyranny of the rocket equation, but I just don't think that can scale to crewed travel.
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