In 1879, the U.S, Mint at Philadelphia made three different Dollar coins: Morgan Dollars; Trade Dollars (Proof-only); and Gold Dollars. Among the Morgan Dollars, the 1879 is popular because it is easy to obtain in all grades, including Gem condition. This date even shows up in MS67, though very infrequently.
Prooflike and Deep Prooflike 1879 Morgan Dollars are actually quite scarce and they represent just a small percentage of the total population. Deep Mirror Prooflike examples are almost twice as rare as Prooflikes.
The strike quality of this date is usually excellent.