They say at the most used cruise speed, the plane will fly at the AOA of the best L/D. And the horizontal axes will be paralell to the relative airflow, thanks to the right incidence angle.
Well, now at wich speed will fly the plane at the most efficient AOA?:
- at Vmd or
- at normal cruise
The most efficient (lowest drag) AOA will be at vmd. If we limit ourselves to aeroplanes at typical unpressurised prop aircraft (low) altitudes, that will be a lot below cruise.
I believe your first statement is referring to the rigging angle of the wing on the fuselage - usually set such that the deck angle of the fuselage is level at cruise speed AOA.
As you climb and the air thins, IAS reduces, and things get more complicated. I believe the average airliner is cruising somewhere around Vmd way up there at 3X,000 ft, but I haven't really looked into that side.