1905. Vienna.
I would act out the cliche and stalk and kill Hitler then return to see what difference it made.
(Despite the fact that my parents probably never would have met, I believe I would still survive as an “orphaned artifact of a now non-existent time-line”. And despite the fact that no other human but me would know whether or not I had made a difference in world history, I would still like to give this a try.)
Probably a Soviet-dominated Europe.