My friend is waiting for me at bus stand; I arrive and I want to ask him about the time he waited for me. How would I say?
How long have you waited for me?
How long did you wait for me?
How long had you waited for me?
How long had you been waiting for me?
How long have you been waiting for me?
You need the present perfect continuous to place emphasis on the duration of the activity and the fact that it has continued into the present (your arrival). So, correct is:
How long have you been waiting for me?
A common, and shorter, way to ask the same question is:
Have you been waiting long?
As you describe the scenario, namely, your friend has been waiting and you walk up and ask the question, you would say, "How long have you been waiting?" You use the present continuous tense because his wait just ended at the time you asked the question.
If you did not ask the question until some later time, like the next day you feel guilty about making him wait and so you ask about this, you would use the past tense, "How long did you wait?", because the event is now in the past.
Usually we only use "had been" when we are discussing two past events, one occurring before the other. Like, "How long had you been waiting before I finally arrived?" Now the "waiting" occurred before the "arrived", and we use the "had been" to express this relationship.
