Well, ceramic is more damaging than tourmaline because it heats up and cools down at a much more intense rate than tourmaline does. Ceramic also has higher heat which can damage your hair if you're not careful.
Tourmaline, on the other hand, emits a lot less heat and its ionic quartz properties allow for more even heat distribution. This is why tourmaline is regarded as the lesser of two evils and better than ceramic.
The plates on ceramic irons aren't infused with any type of protective or ionic minerals, which leaves you open to potential problems from metal ions in the plates leeching onto your hair strands.