I would prefer the word discrimination instead of opinion. Not discrimination in the sense of racism, but in the purest sense of the word:
Discrimination originates from the Latin word: discrīmināre
Which means to distinguish between.
I think that each yogi, all of us, are searching for attaining the highest possible sense of discrimination. When we are capable of discriminating between consciousness and matter, or: between Purusha(or brahman) and Prakriti, we attain salvation through the highest form of vairagya (non-attachment) - Yoga Sutras.
An Opinion, is still a point of view from within the mind. It is something the mind believes or thinks about something. It is a position the mind takes on; a mental stand. Opinion and judgement are one and the same in my opinion .
So when we talk about the difference between opinion and judgement, I see none. When we talk about the difference between the ability of discrimination, or: intellect/buddhi and opinion/judgement, I see a clear distinction. I shall share my view below:
I can be brief by saying: opinion/judgement comes from the egoistic mind while discrimination comes from the higher mental body, the intellect; Buddhi. But more profoundly, I would like to state that discrimination comes from experiencing a hightened state of consciousness. The purer you are, that means; the more conscious you are, the clearer your perspective on things is. You start to see things as they are. Hereby you acquire the ability to distinguish true from false, or truth from maya; illusion. Where an opinion makes you distinguish between right and wrong, which is utterly pointless.
Discrimination and opinion may look alike in form, because they both distinguish between things, but if you picture a cross like this: + : Opinion is the horizontal differentiation and discrimination is the vertical discernment; the latter takes you to new depths.
Opinion is superficial: Changing your mental opinion on things only makes you 'grow' laterally. It makes you fool around on the same level you are already on; no real change or transformation takes place. While highering your state of consciousness and through that process enlightening your buddhi (intellect, the higher mental body) and increasing your insight in what is true and what not; makes you grow in depth, into new dimensions, penetrating reality.
So if nothing else, you may remember this about my view if you will:
Opinion/judgement = distinguishing between right and wrong
Discrimination = distinguishing between truth and illusion
The latter (discrimination) is most useful for teachers; they can address what they see clearly to their students and help them progress truly. Opinion will make you judge your students as being right or wrong in their statement, yogic practice or other actions, while discrimination makes you see what is going on behind the scenes in that particular student. It makes you not only see what their mental stand is, but more importantly; why it is their mental stand and from which dimension it comes from; what part of the students being is active in believing that mental opinion.
The higher your discrimination, the more capable you become of piercing through your students being; you can penetrate his very being with your sharp perception. This allows you for true understanding and helping the student. Not by reacting to the content of his words, because content = opinion, but by reacting to the systems that are active behind the scenes; behind the opinions. This causes immediate and true transformation, instead of a continuation of the games played by the ego.
But what the heck, this is all just my opinion, or.. may it be my ability to discriminate? Who knows.