Nintendo has confirmed that Pokémon X is more popular than Pokémon Y, at least in the U.S. Here are the official U.S. sales figures from Nintendo through the end of December 2013: Pokémon X: 1.63 million, Pokémon Y: 1.54 million.
https://kotaku.com/shreds-of-evidence-that-pokemon-x-is-more-popular-than-1502788351