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.
Definitely a favorite, but it firmly cemented the idea that King cannot write about women and romance. It feels like a cliche attempt you see prodded at on Tumblr where she “breasted boobily down the stairs” or something. Thankfully, the Hulu series took note and, despite the usual degradation most book to TV/film attempts experience, made the romance tangible to the viewers and was overall a success to me. Granted, reading the book clears up a lot questions left unanswered by the series, because of time constraints.