Past I think
The past in hopes that with what I know today I can change the yesterdays making the tomorrow's brighter for everyone.
Future...the past is too full of racism to be enjoyable for myself...
The future, because travelling to the past might risk undoing the current timeline. Also, travelling to the future might provide me with the opportunity to learn something that would be useful upon my return to the present.
Past, because I know that it exists.
Future...its a gamble.