I came across the original three (and Eevee) back when I was a tiny child addicted to Pokemon Stadium on the N64. I didn't really register the fact that they were all evolutions of Eevee, though. Then I came to fanpop and saw this beautiful Pokemon called Umbreon, so I looked it up and re-discovered Jolteon too, then the rest of the eeveelutions from there. :)
So I don't really know which to class as my first one.