I liked Connery. From Russia with Love and Goldfinger were probably two of his best.
I liked Brosnan as well. I felt the series took an upswing to more current film making when he took the helm.
Dalton was a disaster and Moore's antics were campy and seemed so poorly done.
I know TWMIM hates Daniel Craig with the heat from 1,000 suns, but I thought the remake of Casino Royale was very good. The opening scene parkour chase might be one of the best I have seen. And it's like you were going to see Connery or Moore running up a steel girder and sliding from one floor to the other.
I don't think there is a "best" as everyone of them had different traits.
Now, if we are talking government spies who are deadly, fashionable and always get the hot chicks, I vote for Derek Flynt!