Sean Connery > Timothy Dalton > Roger Moore > Daniel Craig > Pierce Brosnan > George Lazenby
Connery's portrayal will always be the best, and the one all future Bonds will be compared to. He played a more gritty and human style of the role.
Timothy Dalton is actually not a bad actor, but I think he got a bad rap. He tried to play the role darker and more gritty, bring it back to how the novels were written. He basically did what Daniel Craig did, but maybe people weren't ready for this at the time. Unfortunately, he also may not have been good enough looking to be a Bond, which many people tend to think.
I grew up watching Roger Moore's. Don't much like the 70's style of attire and music, but he introduced a smooth side of Bond, but Bond became too light-hearted during this phase. Probably nostalgia bumps him up a bit.
Daniel Craig... what can I say? Although he did introduce a flawed, human Bond, I just can't get out of my head that this is what would happen if Gollum, from the Lord of the Rings, got wasted on martinis and threw on a tux. Check out a side by side. The resemblance is uncanny.
Pierce Brosnan was annoying. He played the role as an infallible, perfect playboy, who has no capacity for fear or anything else human.
George Lazenby... not too much to say, though he was closer to how Fleming pictured bond than the rest.