Take your pick.
minute of angle is easy for Americans because it “almost” perfectly works out to 1” per hundred yards. It’s not 1 inch, but it’s close enough to it that for shooting purposes it’s good enough.
Mil’s work with any system. 1/10 of a meter at 100 meters, or 1/10th of a yard at 100 yards. Works with metric and standard. 36” in a yard, 1/10th of that is 3.6 inches at a hundred.
Technically MOA adjustments are slightly finer at .25 inches at a hundred instead of .36 inches, but for any shooting purposes, it’s not enough of a difference to be worth fussing over. That difference is 1” at 1000 yards.
I prefer mils just because everything is base 10 and it’s very easy to do quick calculations, especially if you use meters instead of yards. With a bit of practice it’s easy to tell how many clicks you are off, although it’s not as intuitive right off the bat as MOA is, I think it’s worth the small little hurdle.