My pick would have to be the A Whole Nother Story trilogy, in which (spoiler warning) you can only travel back in time. But because time is in a loop of sorts, if you go before the beginning of time, you will be at the end of time. From there you can go back to any time you want to. And time paradoxes cannot be produced. Plus, your memories from the previous timeline exist as well as the memories from the new one.
I loved the line from the radio version where Ford says, “Drunk in charge of a time ship’s a pretty serious offense. They tend to lock you away in some planet’s stone age and tell you to evolve into a more responsible life form.”
I always loved Yesterday’s Enterprise in (sorry non-book again, but written scripts precede shooting) Trek Next Gen. Mostly non-spoiler version, it revolves around the legend as reported in the Technical Manual of Rachel Garrett and her crew sacrificing themselves to save a Klingon outpost under assault from Romulans. You barely recognize what’s happening at first when a subtle shift in the action happens, and might only catch on and realize it later when things shift again.
Aaand, having read the books and listened to the radio serieses so many time (I read the first book just before the official publication date, as a friend had got hold of an advance copy) it has only just occured to me that that is exactly what happened to Ford and Arthur. Though whether humankind as descended from the B-Ark crowd has ever managed the more responsible life-form bit is very much open to debate.
I also, given this topic, love the time paradox part of how they eventually get rescued by Zaphod by waving down a purely potential ship with Arthur’s towel.