I can find Superman stories i love in almost any age- probably even in the ages where thise on or two favorites would be the "only" stories I can stand.
If i had to choose periods to draw stories from for a "this is Superman" project I'd probably say Siegel/Shuster (1938-1948) and Bronze-Triangle (~1970- 1992's Reign of the Supermen).
And if limited to a single era 1975-1986.