fly between 10000 and 15000 feet.What is, in your opinion, the best setup of the surface and upper visibility?

FWIW, I usually set surface vis to only 20-25 miles and upper level to 25-30. Truthfully, here in the U.S.A. if you set the surface vis to 15 miles you will be even closer to the real world. Only on very rare occasions does the visibility exceed that.

Europe is pretty much the same, 10 to 15 max. Also depending on location, but steamy south might get 10 and Scandinavia get 20 at the same time. 15 is a good compromise. Winters are a bit different. i would recomend 20-30 depending on preferences. Up in the air max 70 but realistically between 50-70.

ThanksWhy by defaults surface visibility is higher than the upper?(100 vs. 75)