Awesome question! Being a history freak, there are so many time periods that I would love to go back to. First and foremost, ancient Greece. I would love to experience firsthand the culture, art, and to fully understand the mythology.
Secondly, I would love to journey back to prehistoric times with the dinosaurs (but only briefly so I wouldn't get eaten!). The dinosaurs were so advanced and it would be incredible to witness their behavior.
I would also love to have been a fly on the wall in 16th century Italy while Michelangelo sculpted the David and painted the Sistine Chapel. Such a master and prodigy of his craft.
But out of anyone that has ever lived, I would want to meet Abraham Lincoln. If only we could all absorb a portion of his knowledge and character, we would all be much better people.