I'd say : it depends .. When you say : "¿Qué tal? You use it when you're talking with your friends ,people around your age or known people. For example : at School. ¿Cómo estás? That's when you want to know more about the situation of that person. For example: your best friend. Moreover , I'd say with respect : ¿Cómo estás? ¿Todo bien? When I don't know that person and because we don't know each other. He will say : I'm fine. That's all.

When you want to start conversation or interaction with someone, especially with someone new you can just say QUE TAL! and you can get the answer BIEN or even QUE TAL QUE TAL - QUE TAL It's just that when you want to interact with someone you don't want to know exactly how they are, how they feel so that they start bothering you with their issues. So QUE TAL is the best way to start interaction. When you want to go much further in interaction you can say COMO ESTAS? and the other one you are talking with will know that you have time for him, you want to interact more friendly... so Como estas? Estoy bien, tengo examen... Estoy poco nervioso... me pasa algo blabla

Hi Steven, ¿Cómo estás? - How are you? ¿Qué tal? - What's up? Cheers!