Friends Ok is generally used in informal way of speaking or writing any message or letter. In case of any formal discussions or letters, OK is not used. Do you all agree with me?
Wrong, OK is an accepted word which is used in formal communications too, at least in corporate world, we use it a lot since it is a very clear and expletive confirmation of positive response.
It is not frequently used. They generally use the words like "Confirm, Agree, Right, Approved, etc.".
"Ok" is generally used informally .
I am reitrating again, OK is an accepted form for positive response and confirmation in Formal communication. I have been working for the last 15-16 years in corporate world and the word is freely used everywhere FORMALLY. All the other terms you have given are used too but OK is more frequently used.
"I am free of all prejudice. I hate everyone equally." - W. C. Fields :)