Black 2/White 2. Disregarding those direct sequels (since I don't count them as a third version), either Yellow (which I voted) or Crystal. I never played Emerald or Platinum (but my cousin has played both of them).
Also, you should of add Blue (Japan) to the pull since Pokémon Blue Version is the 3rd Pokémon game in Japan of the first Gen (while Yellow was their 4th game of Gen I).
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