One era I'd like to go back to is before December 1913, to stop the Federal Reserve system from being created. Since the Fed was established, our economy has become dangerously overdependent on reckless Wall Street speculation, and Forex manipulation that needlessly devalues the dollar on even the most minor things. If it weren't for the Fed, the dollar would still be on the gold standard today, at $20.67/oz of gold (as it had been from 1792-1933).
Absent that, I'd like to travel back to the late 1940s, when America was beginning to go through a boom period following the end of World War II. (Of course, I'd eventually be carted off to Korea and then Vietnam.)