This was a toughie. First, I'll second the assertion that "best" (thread title) and "personal favorite" (OP) are
not the same thing.
So I went for my traditional personal favorite and voted for Timothy Dalton. As a fan of the books, I appreciated the effort that he put into bringing that version of the character to the screen, and I'm happy to see him getting some love here. Nevertheless, over the years I've come to see his shortcomings in the role while better appreciating what each of the other official Bond series actors brought to the role.
Sean Connery: Being a fan of the books, he's not the no-brainer choice to me that he is to so many others, but there's no denying his archetypal place in the film series or the pure charisma that he brought to the role.
David Niven: Seriously? "One of these things is not like the others...."
George Lazenby: Not a great actor, but I found him to be a refreshing alternative to the "Big Two" back when Moore was the current Bond, and he has the virtue of having starred in my absolute favorite film in the series. My dream Bond film would be OHMSS starring 1987's Timothy Dalton....
Roger Moore: He was easy to dismiss back when he was the current Bond and I was longing for a more Fleming-based approach, but the man and his films were always highly entertaining in their own right. What's more (especially considering some of the casting choices that the producers flirted with in the early 70s), I've come to greatly appreciate Moore's role in proving the longevity of the franchise beyond Connery, shepherding the role through seven films and the better part of two decades...thus ensuring that the series would live to see more Fleming-evocative days.
Timothy Dalton: For all that I loved about his take on the character, I've come to see that his shortcoming was that he was
acting the role, but he wasn't
owning it. He lacked the raw charisma that most of the others brought to their varying takes on the character. (A shout-out to
Lapis Exilis if she's still around, as it was a post of hers several years back that brought me to this realization.)
Pierce Brosnan: When he was the current holder of the license to kill, I considered him to be perhaps the best "whole package" Bond...but he suffers a bit in hindsight for the films that he was in.
Daniel Craig: I really enjoy what he brings to the role, but I don't consider him my personal favorite. Whoever comes after him will have big shoes to fill.
Diamonds set the campy tone for Bond in the rest of the '70s, though admittedly much of that comes down to acting and directing choices
And writing...IIRC, DAF and LALD had the same screenwriters, contributing to the feel that the former has of being the unofficial first Moore film.