Probably the 70's, 80's or 90's since I'd still have vaccines and some technology and all. Witness the dawn of the internet as someone who knows what it will become. Plus, phone freaking was still a thing, I'd do a lot of that.
If I could keep my knowledge, or at least keep my level of education, I would be born in the late 1800's. Be around for the birth of modern physics, find a way to profit off of Russian Revolution, generally bool around for a while.
So many choices! As far as America is concerned, I think it would be fun to either experience the Wild West (Yeah, I know. It's cliched and overrated, but I stand by this.) or any time between the 1950s to the late 1990s. I'd love to experience pre-cucked America. Warts and all.
I also think it would be cool to experience living in either Victorian Britan or Bakumatsu Japan. I know that's autistic, but whatever.