I would actually try and see what is available for free online as she wrote a lot of short poems and stories, which could give you a good preview. I just finished the short story "Mr Durant" and it was very well done. "Arrangements in Black and White" is a popular lit class read but for good reason.
Honestly? I'd actually say "Enough Rope." I haven't read all of her work, but it's her first book of poetry and her personality really comes through in it. She's clever, sarcastic, and is readily able to make fun of the world around her.