Past - I always said I was born in the wrong time period. Would love to be able to help end suffering in different simple ways. To see historic events happen as they happened. I would like to see the world and the US before it was all settled and strangled by laws that restrict human freedom. The past would be stable (I assume going to the past you would not be allowed to alter the future).

Going to the future - doesn't seem applicable. Things in the present directly affect the future, so the future is not stable at all and may not even exist, or may change so drastically moment by moment based on what happens in the present that the future would be a miserable place to be.

The past is stable. And we already know our history (or do we - going back would answer A LOT of questions for me...).

Interesting question.