How far back in time could you comfortably go? The main emphasis I have in mind is that cultural, political, economic, technological, etc. situations changes from today. Other aspects of this question, particularly personal matters, you can interpret however you wish (e.g. you can assume that everyone you know is also transported back in time accordingly as they are, or perhaps people's age, deaths, births are changed according to the era you choose; if you are of a certain profession, perhaps you would assume that you are specialized in an earlier version of your profession, or you would be of another profession entirely if yours or a predecessor did not exist at the time; you may choose any particular location in the world with a given era; etc.).
Included is a poll that perhaps has too many options... but possibly there are a few of us who would genuinely want to go back to the prehistory era? And the poll will be increasingly outdated starting in 2030 onwards (assuming the forums still exists by then).