A few choices here to suit your tastes. If you can do it, start with Pantagruel and read right through(!) Pantagruel was written first, but has traditionally been placed after Gargantua, which is a "prequel."
Here are three strategies for reading this book. Try the one that works best for you:
A. Start with Gargantua from Chapter 23 to the end. Then move on to Pantagruel, Book IV.
Gargantua, Prologue and chapters 1, 3-8, 14-17, 21-32, 34-36, 48-58