On most of the earliest versions of 1873 coins, the 3 of the date looked more like an 8 because the loops of the 3 were so close together. This was changed later in the year, creating two major varieties: Closed 3 and Open 3.
The Open 3 variety appears to be twice as common as the Closed 3 variety, per the PCGS Population Report (as of July 2011). The 1873 Open 3 Cent is readily available in all grades up to, and including, MS-64. In Gem condition, any 1873 Indian Cent is scarce; the Open 3 variety becomes very rare in MS-66. None have been graded higher.
The population of Brown 1873 Open 3 Cents is less than that of Red-Brown examples, but that is due primarily to the lower value of the Brown versions (which does not always justify getting them certified).