Time travel...

Let's play "Would you rather..." Would you rather travel back in time, or travel to the future?  Elaborate.

You have to pick one or the other, not neither or both.

Would you go back and change something you've done?  Would you go back to see Stonehenge being erected?  Would you go to the future to see where you'll be in twenty years?  Would you go 100 years in the future to see if we've survived as a human race?