Undoubtedly, I would pick time travelling. Although the argument against time travel is that you could irreversibly affect the future (either for good or for bad), my counterargument is that, based on the same philosophy, whatever changes are made were meant to be. Destiny cannot be negatively or positively affected by human actions because "destiny" by defintion is "a predetermined course of events".
Time travel is much more useful than teleportation. In fact, teleportation would be unnecessary if time travel existed. If someone had the ability to travel back in time to prevent a disaster from happening, why would teleportation be necessary? Additionally, time travel inherently includes an infinite amount of oppportunities to correct situations. If you don't fix the problem the first 10 times, maybe the 11th time will be the charm. Think "Groundhog's Day". Also, if you were equipped with the ability to travel into the future, you'd be able to travel back to the present (or the past) to prevent bad situations from occuring.
That all said, time travel is a much more potent superpower. Sure, teleportation could be used to hop from place to place for FUN, but if it's being used for leisure purposes, it can longer really be considered a power.
A super hero with the ability to time travel would most certainly be at a greater advantage than one with the ability to teleport. For instance, if a teleporter pops up and foils my plan, I could just rewind the clock five minutes, wait for him/her to show up, and take care of business.