I'd hate to spoil the fun for y'all, but time travelling to the past is impossible, and travelling to the future, when talking technologically, would take thousands, possibly millions of years for the technology to be perfect. Basically, you'll need to be able to travel faster than the speed of light. It's kinda hard to explain the scientifical crud behind it, but I do know that once you get out of that speeding vehicle/machine/whatever, years would have passed. Welcome to the future homie G! XD
And since we're only having fun here and ignoring the laws of physics, I'd like to travel to the future. Sure, there might be a chance of more pollution, or maybe the ozone layer would've been completely destroyed, but who knows, some genius might've figured out a way to restore the ozone or to prevent serious ultraviolet rays from the sun. *coughcoughdropanicecubeintheoceanliketheydidinFuturamacoughcough*
Besides, it'd be interesting to see some of the technological advances that mankind has invented. You might even catch a glimpse of Fry. XD