Hi Ing. The question should be: What is the correct answer 'to' "How have you been?" The question is asking about the past. It is usually asked if you haven't seen someone for a while. The reply might be: I have been fine. You might also say: How have you been this week? I have been fine. I have had a good week. Thanks How have you been lately? I have been fine. Thanks. How about you? So, it is asking how you were previously. It is different to asking "How are you?" which is asking how you are at the moment of asking.

I have been... (great, busy, fine... etc ) I vote for GREAT ! -How you've (you have) been? -I've (I have) been great, thanks ... you? =D

Great! Couldn't have been better! I've been quite fine.

In conversation, it is understandable. In writting, the first letter in a sentence must be in capital letter, period. By concept, " how have you been?" is only a compliment, there is no special answer for it. Any answers are correct answer even it is out of the question. How have you been? (you may raise your voice to make a cunter question) Still surviving, how about you? All answers given by others are correct. My answer is a suppliment to their answers, it is not traditional, you may not found them in books.

depends on your mood