I am a Sinnohan, but if it would have to be one game.... it has to be a Unovan game, and it doesn't matter if it is Black or Black 2 (white or white 2 too). I really enjoyed journeying across Unova and enjoyed the story very much.
It was exciting as a child to see moving Pokémon sprites, and all. Anyway, Unova. Nothing else matters.
I love PMD as well, but Unova had a bigger impact in my childhood, and I enjoyed it more than I did PMD EOS :|