If you don't do a direct A-B comparison, then I don't think you can tell for sure which optic is best. The memory is not reliable on fine details. That being said, your eyes are your reference. If a particular binocular is very decent, or very bad, your eyes will tell you based on what you see in everyday life. To judge two great binoculars against one another, you need to see them both together, or A-B them against a known reference. After you find the the optic that best suits you, you will find that it won't be best for everyone else. It depends on which set of compromises or strengths are important to the individual. Just my opinion for what that's worth.
Bruce
Once you have done ALOT of comparisons you remember what was best when you compared them though. I have compared alot of alphas side by side and decided waht I liked best. My results seem to compare with all the major reviews so I think I am in the ballpark. When I get a new glass I compare it to what I know is the best and arrive at a ranking for them.