This has become the ultimate superpower would-you-rather among my friends recently, and I wanted to see how GT fares with it. If you were offered one power or the other, which would you choose and why? YOUR ANSWERS SHALL REVEAL MUCH ABOUT YOU. Some stipulations below:
1) Neither option will prolong your natural life, other than allowing you to escape deadly/dangerous situations.
2) You cannot do an end-run by time traveling to a future where shapeshifting technology exists. (Nor can you shapeshift into a time machine — see #3.)
3) You can shapeshift only into living things (I was going to restrict this to Kingdom Animalia but if you feel the need to experience life as a mushroom, rock on with your bad self, fungi are awesome).
4) You can't fuck up your own/the world's timeline through time travel, though you will be able to interact with people in the past/future (no killing Hitler, no accidental self-erasure). Explain this with any timey-wimeyness you feel is necessary, but them's the breaks.
ETA 5) Time travel also allow you to travel through space. You can travel to 1920s Paris from Colorado, if you like.