Though the unbridled Pokémon craze of the late 90s (Pokémania, if you will) could have been mistaken at the time for a fad, the series has proven itself to be an international, cross-media cultural touchstone. The latest evidence of this evolution comes from Famitsu, by way of Yahoo! Japan, which reports that the main series of games have crossed the threshold of 200 million units sold (in fact, by the end of February, they hit 201 million). This doesn't include spinoffs like Pokémon Snap or Pokémon Mystery Dungeon, which bring the figure to 279 million.
The last milestone of this sort came in 2005, when the series hit the 100 million shipped mark, according to this GameSpot article from the time. Considering the series began in 1996, that (very roughly) means nine years to sell the first 100 million and 11 years to sell the next 100 million. Though sales have slowed slightly, that's still a remarkably steady performer in an increasingly tumultuous video game industry.
Also, Arceus created the universe of Pokémon and without him no other Pokémon would exist and so by extension he is the best Pokémon so please don't comment about Mewto anywhere on this post. Thank you.