I would go with invisibility. Time travel can mess stuff up.
EDIT: I'm glad this is back. Many memories in this thread.
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I'll pick time travel so I can go to a point in time when invisibility generators are one cent, buy that. And then I'll have both of them. OHH OHHHH I DID NOT JUST SAY THAT!!!! HOLY SHIT!!!!!!! YOU JUST GOT 2340 TRICKSHOTTED