What's your favorite class?

Question

1. It's a math class.
2. It's math class.
3. It's math classes.
4. Math class is my favorite.
5. Math classes are my favorite.
6. A math class is my favorite.
(Which answers are correct? Are all correct?)

Answer 1

They're all correct.

However, in the U.S., # 2 and 4 are the most common.