Re: When was the manga, in your opinion, at its peak?
I voted for the whitebeard war saga but thats only because it is the most recent completed saga. Each saga keeps getting better and better so a new peak is always on the horizon.
As far as my favorite saga I would say it was the Baroque Works Saga. Mostly because the grand-line seemed so vast and interesting not to mention a bunch of great characters such as robin and ace where introduced in that saga.