Through its latest earnings release for the nine-month period that ended in December 2017, Nintendo has revealed sales for its most popular games of the year, including multiple Pokémon games. As of December 31, 2017, Pokémon Ultra Sun and Ultra Moon have sold 7.17 million units; Pokémon Sun and Moon have sold 16.05 million units; Pokémon Omega Ruby and Alpha Sapphire have sold 13.94 million units; and Pokémon X and Y have sold 16.26 million units.
Nintendo 3DS
Pokémon X/Y – 16.26 million units (Up 0.06M units)
Pokémon Sun/Moon – 16.05 million units (Up 0.14M units)
Pokémon Omega Ruby/Alpha Sapphire – 13.94 million units (Up 0.09M units)
Super Smash Bros. for Nintendo 3DS – 9.16 million units (Up 0.25M units)
Pokémon Ultra Sun/Ultra Moon 7.17 million units
Pokémon Ultra Sun & Ultra Moon
Pokémon Ultra Sun/Ultra Moon
Japan – 2.37M units
Overseas – 4.8M units
Global LTD – 7.17M units
Source: ResetEra
Pokémon Blog 