Connery was the first actor to portray Bond in the film franchise.
The Bond film series produced by Eon Productions began with the release of "Dr. No" in 1962, starring Sean Connery as MI6 agent James Bond. As the first Bond, Connery established the character and set the bar against which all future Bond’s will be measured. Without Connery, there may never have been a franchise.
Many of Bond’s iconic lines and traits can be traced back to Sean Connery. He immortalised the idea of Bond enjoying his martinis “shaken not stirred,” and first delivered the iconic, “Bond… James Bond,” introduction. Without Connery’s impeccable portrayal of Bond, it may never have evolved into a franchise. It may have been reduced to the graveyard of charity shop bargain bins as a one film monstrosity. In this regard, Connery has to be considered the best Bond because, without him, there would be no cinematic Bond. 
Connery is a good actor. He is a great action hero. But he is not Bond. Fleming was reportedly aghast when he first met him and called Connery an “overgrown stunt man”. His image of Bond was not of a brawny tough-guy walking around with a ‘Scotland Forever’ tattoo.  Bond encapsulates more than good looks and muscles. He has to be sophisticated, charming, humorous and cool. Connery is nothing more than an action hero.
[P1] Connery was the first Bond. [P2] Therefore, he set the standard against which all other Bonds are measured. [P3] None have come close since.
[Rejecting P3] Others have brought far more of Fleming's Bond traits to the character than Connery.