Ron Guth:
The 1878 Dime would appear, at first impression, to be a common coin, but in terms of the number of certified survivors, it is actually less common than the 1880 (with its mintage of only 36,000 pieces). On the other hand, the 1878 Dime has a population comparable to that of the 1877, which has a much higher mintage of 7.31 million.
Most certified 1878 Dimes grade MS-64, followed by MS-63. The finest PCGS-certified examples (based on the November 2011 PCGS Population Report) is a single, amazing MS-68.