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.
Hyperion.
Without a doubt, Hyperion.
A Gift of Time by Jerry Merritt is about an old man at the end of his life that has a space alien crash land on his property. He assists her in repairing her ship, which as it turns out travels through time and space. As a reward for his assistance, he is allowed to ask for one gift. He has his current mind placed into his childhood body, so that he can be there to rescue his little brother that was kidnapped that Summer.
It’s a really good book in my opinion.
Although not exactly time travel, a similar concept is The First 15 Lives of Harry August by Claire North. It’s about a man who is effectively immortal. He dies and is immediately brought back to the beginning of his life. His conscious memory of his previous lives comes back when a child begins to have self-consciousness at around 3 years old.
Really interesting Time Loop type story.
Lots of good ones mentioned here. I’ll add Replay by Ken Grimwood.
Timeline by Michael Crichton. He did the multi-verse time travel idea before it was cool. /s
Seriously though it’s my favorite book
Homestuck got a physical book release so screw it, I’m going to say Homestuck while making fierce, belligerent eye contact.
Buired 500+ comments but Millennium and Mammoth by John Varley are absolutely fun rides. Nothing too deep, or too mind blowing. But holy shit they are fun.
All of an Instant by Garfinkle, Richard.
Shining Girls. One of the best books I’ve ever read. The miniseries was terrible.
Heaps of great ones here, and some I need to add to my list.
I’ll add a couple that come close to being time travel, but I guess are more like time dilation stories -
Tau Zero by Poul Anderson, about a group of colonists on a ship that is accelerating towards the speed of light, only for a catastrophic failure to cause the ship to become unable to decelerate - leaving them to accelerate forever into space.
The Inverted World By Christopher Priest - A dystopian world stretches out in all directions, and in it a massive, decaying city on rails creeps forwards. Time accelerates out into the past behind it, causing increased passage of time and age for anyone back there - but the future stretches out in front, slowing down time for anyone who moves too far ahead. Everything must move at walking pace, and tracks pulled up behind the city before they rust and buckle, to be laid in front so that the city can keep moving forward, into the present.
I’m really shocked that it hasn’t been ripped off to death over the years, but Time and Again was a unique take that still kind of stands on its own.
Cloud Atlas.
I just finished Before The Coffee Gets Cold and I love how time travel is approached there! It’s such a different take from all the super complex wormholes seen in sci-go given the rule that you cannot - no matter what - change the present. I also love the message that it passes on, to cherish what we have now and understand the delicate circumstances that led to it.
Beautiful little book
outlander going through standing stones with gemstones to travel in time, sometimes using a ritual sacrifice. I found it interesting and a good plot point for most of the books. Interesting things happen in various time periods.