What’s the best choice: Okay vs. O.K. vs. OK

Which version is “right”? Any one of the three is acceptable. However, whichever one you choose, be consistent by using only that spelling of the word throughout the manuscript. 

Personally, I prefer O.K. over OK and okay. OK also is an abbreviation for Oklahoma, so there is the potential for confusion in using that spelling. Okay takes up more space, and my prejudice is against longer versions of a word when shorter versions will do.