Hi, Chick on the Beach!
Carrots are better. Pumpkin is allowed on Phase 2, but according to the GFGCG, you can only use 1/2 cup and it's "Very Limited"...so I would go with carrots.
Soup sounds great! Enjoy! (and check out the extensive soups and stews for both Phase 1 and 2 in the recipe forum)