Re: When was the manga, in your opinion, at its peak?
Honestly the War saga was the best I've seen so far. The pacing, twists, action, excitement, and WOW factor were all there, and in unison with each other. I recall leaving work early some days just to get home and read the latest chapter. Now....not so much.
I don't particularly have anything against the post timeskip storyline, except the pacing at some parts, but the Whitebeard War was the best arc to date. I wouldn't call it the true "peak" however. More like a tremor that predates an earthquake.