Only share one recent strategy even though you might have multiple. You can go overboard and go on a tangent discussing too many favorites. Keep the reasons simple and short.

I would avoid spending too much time on this answer. The point is to be memorable and if you go into a long story on why it was your favorite then you can lose the interest of the interviewer.

"One of my favorite strategies was working with a client who specialized in the (insert industry name). They were working on a strategy for their (product name). I enjoyed working on it because I learned so much about an area that I thought would be boring to me. It's still one that I bring up as an example when working with clients in a similar industry."