To me, it is 1921-1928. You had the venerable wheat penny, the unique Buffalo nickel, and the beautiful Mercury dime, Standing Liberty quarter, Walking Liberty half, and peace dollar. What is your favorite era?
I think 2001-2013 is my personal time period, because that is when I started collecting (AGAIN). All those beautiful coins that the OP mentioned are prized designs, and are an intrical part of my current collection.
I have to admit - reluctantly - that from 1916 to 1932 the US Mint finally got the artistry and the industrial processes all right. But what about the paper money? Would you agree that the National Bank Notes of the First Charter Series were the epitome of art for that medium?