David Akers (1975/88):
In terms of overall rarity, the 1871-S is very similar to the 1869-S, 1870-S, 1872-S and 1873-S among others. As is the case with most Double Eagles of this era, the majority of 1871-S twenties are in EF or lower grade. A strictly graded AU is very scarce and mint state specimens are decidedly rare. I have seen a very small number of average quality (Unc-60) examples of this date as well as two or three choice specimens. I don't recall ever seeing a true gem (Unc-65 or better) but it is certainly possible that one exists in a collection somewhere.