I'd be leaning towards Pokemon, but I'm trying to work out which generation (not to mention that they're made in pairs... Damn you, Nintendo!) First gen in Kanto was the classic, and perhaps that should be preserved? But second gen had both Kanto & Johto, and was just so much improved. On the other hand, 3rd gen in Hoenn had more improvements, and still stood relatively well on it's own... Remakes are also tempting, but fuck any of the new ones from 4th gen onwards, they're acceptable as a continuation of a series, but not as the sole surviving game in existence.
So, solitaire.