General antonyms:
* Simple
* Basic
* Unsophisticated
* Naive
* Rudimentary
* Unrefined
* Primitive
* Uncultured
* Uneducated
* Unskilled
Antonyms related to specific contexts:
* Crude (referring to manners or behavior)
* Unsubtle (referring to style or approach)
* Clumsy (referring to skills or abilities)
* Childish (referring to maturity or understanding)
* Unworldly (referring to experience or knowledge)
The best antonym will depend on the specific context in which "sophisticated" is being used.