It doesn't matter which one you pick up. They're all brilliant.
She won the Pulitzer Prize and the Nobel Prize for literature. She is my favorite living author (and perhaps favorite author ever).
To get you started (say, if you're busy and can't leave immediately to go get a book) read this. And listen to it, too. It's absolutely worth your time. Her voice is perfect for storytelling. The links are to her Nobel lecture. It is incredible, and all about language.
I also love the fact that she begins her Nobel lecture with
"Once upon a time..."