So many decades to choose from. I honestly can't narrow it down. A chance to observe things in predynastic egypt would be interesting. That's a period that's really fuzzy in the history books. There's a lot missing from 3rd century Roman history as well. And what is there, is badly covered.
What else? Oh! Some of the visgothic history around north africa in the 5th and 6th centuries. How about Asuka or Nara period Japan?
Would I return? Absolutely. I would be there to observe. I like my creature comforts. Bring me back to my couch and my PS3 eventually.
I dont think I would take anyone with me either. My partner in crime would not handle the squalor and illnesses of a previous age well. If I was going to bring someone with me, it would be someone who could handle firearms.. just in case we get into trouble and need to hold off the rampaging hordes with a few futuristic tricks ("This...is my BOOMSTICK") until I can get the portal set back up to get back to my own time.