IB Interview: Best Response to "What is Your Greatest Strength?"

I'll be taking a non-traditional route to banking (graduated a large state, non-target school, have previous professional experience in public accounting, only way ill be getting in is via networking). Before I interview, I like to have a general idea of what my response will be to certain questions which are likely to be asked.

"What is your greatest strength?" is one of those questions.

When posed this question, do you think it would be more prudent to respond with an answer that is either:

a) directly related to past professional experience (ie. I've worked in a client services industry before and understand the demands of such a business- being available on-demand; tight deadlines; client/seniors say jump, I ask "how high?", etc)

or

b) a "softer" personal characteristic (ie. I'm "dedicated" or "highly motivated"- both are traits which I can also substantiate using quality professional experiences)

Insight and anecdotes are appreciated.