I guess it depends on what kind of fantasy and sci-fi you're into. I always like to recommend The Secret Sea to self-avowed SF/F fans. It's got kids as the main characters, but in the same way Salems Lot has a kid as a main character, you know?

There are also the Flash books and the Thanos novel, if you lean toward comic books at all.

And my latest -- UNEDITED -- has some sort of avant garde speculative elements. I wouldn't call it SF/F, but then again, I'm not sure WHAT I would call it!

Oh! And if you like near-future stuff, there's The Hive, which I wrote in collaboration with my wife. (And she didn't leave me!)

Jesus, you asked for "one" and I listed a dozen. I suck. 😂🤣