“One of the best” is correct and “one of the bests” is incorrect. “One of the best” means that out of a selection of events, people and things, this one ranks in the top three.
We had a great party, it was one of the best parties ever!
One of the best
“The Best” is the superlative adjective of the word “good”. There is no plural of “best”.
We use “One of the” when we want to say something is close to the highest superlative but leaves room for other elements that may also be considered of the highest or lowest order.
Cristiano Ronaldo is one of the best players in football.
When you say “one of the best” instead of “the best”, it provokes fewer arguments as everyone can agree that Ronaldo is one of the best players but allows other people an opinion of who they think is the best player.
One of the bests
“One of the bests” is incorrect in English. The reason people say “bests” in English is that “one of the bests” implies that there is more than one person involved. Most nouns add an “s” to make the word plural but it is important to remember that “best” is an adjective and therefore does not add “s” to make it plural.