I guess I like both. The older generations remind me of how much fun I used to have as a kid, which is something I don't get from the newer games; they're enjoyable, but they've lost that spark of excitement...or perhaps it's just me growing old and bitter. But I would most definitely not attempt to play them now, because the Gameboy games are extremely slow and clunky when compared to their updated successors. I'd rather play HeartGold than the original Gold, for example, both for the new features that have been introduced since Gold included in HeartGold, and because the former is significantly more polished.
The funny thing about nostalgia is that it's never as good as you remember it to be if you actually try and experience it by doing it; it's better as a memory. I'm quite content to look back on older generations with fondness and see what the new ones bring. The older Pokemon are in the newer games anyway, and if I really want nostalgia, I can just play through the game with a team of my old favourites, like I did in Black.