For my most nostalgic book series, I'd choose the Redwall Series by Brian Jacques. It was one of the first series I got seriously into, and at one point I had all of them collected (I think they're in a box in my parents' house right now). Sure, they get formulaic and samey after a while, but they're comfy reads for me.

For my favorite recent read, I'd probably choose Bunny by Mona Awad. I'm a huge fan of the "weird book" genre and this book came up over and over as a suggestion so I picked it up. And oh boy is this book a wild ride. I enjoyed it, but I'd add a caution that I would proceed with caution if you are prone to psychosis, because at the end it made me feel like reality itself was unwinding.

One of my favorite authors of all time is Akaweke Emezi, and my favorite of their work is The Death of Vivek Oji. Reading it fully tore my heart apart, and then taped a few pieces back together.