Fine, thanks. What about you?
There's nothing wrong with your answer, although it might get tiresome if you word it exactly the same way, every time you're asked. But the solution for that is to merely use a few simple variations:
I'm doing great today - and you?
Doing well, thanks. How about you?
Not bad, yourself?
Thanks for asking, I'm doing fine.
I think it's usually best to avoid clever responses to such a standard question, particularly when you're with new acquaintences. Sure, you could reply with something like, "I'm happy as a clam," but that's not very professional, and it would probably undermine your credibility rather than enhance it. Such jocular ways of answering are best left said among close acquaintences when everyone is kidding around.