Would the rest of the fleet be aware of what kind of crap Spock has pulled, though? Would Starfleet publicize the events of "The Menagerie" and "Amok Time", among other episodes? Obviously there would be rumors, since people were involved indirectly in some events (the computer tech that tried to stop Spock in the Starbase 11 computer center, or Commodore Mendez's secretary), but would many people in or out of the service learn of these transgressions? I don't think so. So maybe that's why he's still "the best".