Hello ElCid I'm an English learner from Japan. I know I myself am not good at English. But if you don't mind, I'd like to try to answer your question.
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1) Say the same thing twice over.
2) I know him best or I know him well. I know him very well./quote>
I think that to say "I know X best", you need at least two individuals...
EG: "I'm aquainted with all the members of the staff, but I know Mr Paco best", or "it's Mr Paco I know best".
What do you think?