I have tried several, and they will eat them for a bit, but lose interest rather quickly. They like their cat food. Thomas and Beau seem to have sensitive stomachs, so I just stick to cat food they like.
Evie likes apples and will eat anything that falls on the floor. She also seems to have a sensitive stomach, so we don't give her much besides her dog food and treats. She also likes plain popcorn, and that doesn't seem to bother her.