What is a Most important Keyword we have optimized for?(Question for each seo expert?

Hello all seo experts. This subject is for each one. What is a many vital keyword we have optimized for? Please place a website couple additionally if we do not have any complaint ? we hold a singular word keywords have been a many rival ones as well as we am certain there have been many experts here who has finished seo for singular word keywords.
Lets see who has optimized for a many rival keyword?