If you had a time machine that could take you anywhere in time and back again once, and once only, what time period would you go to?

I'd go back to the time of the dinosaurs. My sons have developed an interest, bordering on an obsession, with the wee beasties and this has rekindled the interest I had in the things when I was a boy. I'd love to find out what they were actually like, and end the speculation once-and-for-all.

So where would you go? Past or future?