What is the best first baby food for a sensative tummy?

We took our 5 mo old off baby food for the second time since she still gets a sore stomach. She cries and spits up. I decided to wait til she’s 6 months before trying again. Since she seems to have a sensative stomach and she always had some gas problems, which food should i try when I start her again? We tried sweet potatoes and carrots so far, both upset her. Right now she is still eating rice cereal. which food is the easiest to digest?