Here's a breakdown:
* Caul is not a Spanish word. It might be a misspelling of "cuál" which means "which".
* es tu preferida is grammatically correct but incomplete.
To make the phrase correct and understandable, you need to specify the context. For example:
* ¿Cuál es tu preferida? (Which one is your favorite?)
* ¿Cuál de estas es tu preferida? (Which one of these is your favorite?)
Please provide more context, and I can help you translate it correctly.