Carter was a dunce completely inept at macro economics.Ah! The Carter years! Inflation, gas lines, energy crisis and The BeeGees.Since you confine it to twenty year increments, probably the mid 70s. Personally I'd say more like 1966.
You weren't alive then, were you? I was matriculating at The Ohio State University during the mid 70s and I can tell you that that era wasn't the benchmark for American greatness.
My guess The Donald thinks that the late 1940s, after WWII and the birth of the Cold War was America's greatest time. You know, while Harry Truman (d) MO. was president.
For my money, the early 1960s right up until 1968, a year that held too much history, was the greatest America I have lived through.
While Reagan was asleep at the switch, his handlers managed a deficit deal with Tip O'Neill that gave us both guns and butter and thus stimulated the economy in spades.