Others have mentioned about the coatings, nirtogen filled, precision glass grinding. These are all important for good glass. What sets "best" way apart from good is the precision in the mechanical aligment of the two separate lense systems (right and left) and the ocular and bell alignment. Is both sides moving the same distance at the same time when adjusted? And is this repeatable? Is the adjustment smooth and responsive? Or can you turn the adjustment wheel and not see the image change right away?
The other important features is the way the glass receives the final polish and the coatings on internal mirrows.

Any bino company can coat lenses and fill with the tube with nitrogen or other inert gases (such as argon) and grind good glass. Its how you finish the glass and align it that counts.