They both sound completely destructive to a human mind, but while the second one would probably lead to a lot of obsession and paranoia about going back to the exact right time and choosing out of many trivial decisions for their subjective merit, the first one would either overwhelm and kill (and/or enlighten) me, or cause me to transcend conscious thought and become some kind of god on earth. I'd go for the latter. It feels like the premise for a Lovecraft story.

Would you rather have a chance to successfully date someone you find very attractive, or guarantee that your eventual death will be painless?