Preferably, any time before modern technology.
I would say sometime around the Golden Age of Piracy. The world was ripe for the taking, the population was not nearly as high as it is today, and there was so much to explore. Nowadays, most of us are living our lives by going to the same dreadful job every day, only to go back home and not do anything significant with our lives. Every land is owned and there isn't much left to explore anymore.
Yes I realize there a many downsides to going to the past (disease, famine, the risk of death at every corner), but I feel like life back then was much more peaceful without the strains of modern technology. People got out and explored more and enjoyed the sounds and sights of nature. Nowadays, people can't seem to go a second without their damn cellular phones or other devices!