Who or what determines which is considered the "best translation"? And by what criteria? In the men's fashion set of examples for translation, for instance, in an example about safari style, the translation offered as "best" is gibberish - poor English grammar, using many Spanish words not found in the English language, taken directly from the material to be translated.
When we are given translations to score, the best translation isn't necessarily at the top. If you click 'show more translations' and go through marking all of them then you will see what scores other people have given them. Sometimes the best translation with the most upvotes will be halfway down the page. When you find a bad translation, just mark it down and the Duolingo magic will do it's job and eventually the good ones will work their way to the surface.