Totally completely 100% personal preference. There is no realy "best" when it comes to expo. Its about what feels right and provides you with the best control to get the performance that you want.

I will say one thing that expo will provide and that is consistant "feel" between low and high rates.
That is, you add expo on your higher rates so that the control surface response has the same feel (and actual movement) between low rates and high rates. On 9C and higher end Futaba radios you can actually see a "curve" graph on the screen. This allows you to actually see the stick responce via the graph so that you can match the response EXACTLY where you want it but still get the big throws when you need it.