Why do some sites say I'm a metal monkey while others say earth one?

Because there are two ways to figure out a person's element. First, a person's element can be found based on his/her zodiac. That's why your element is metal. Second, Chinese fortune-tellers can tell a person's element according to his birth year. That's why your element is Earth.

Both are right. However, if you seek fortune-telling, then you'd better take Earth as your element.