There isn't a "best" setting that works for everybody. If there was, there wouldn't be a setting, we would have used the "best" value as a fixed value, instead of making it user-settable.
As everything in FSX, the setting that works best for you depends mostly by the combination of your hardware, your other settings, the combination of add-ons you use, and your willingness to compromise VAS usage, smoothness and fps. And it will not be the same for every scenery too.
Note that, since it's not a setting related to FSX and the FSX.CFG, you can apply it and see the result immediately, without restarting FSX and without having to Save the settings.