Francis muisyo

It all depends on the situation. But, for the most part, "Thanks" is informal, while "Thank you" is more formal and polite. Saying "Thanks" to someone sounds like you are in a rush and that you're not as appreciative as saying "Thank you". Also, "Thanks" indicates that you are less inclined to understand the issue at hand. Saying "Thank you" is a firm and direct response, meaning you mean what you say and both parties know exactly why you are thankful