Pokemon Red :B
But I love HeartGold, I played it while playing Red, and I have to say I enjoyed HG more. I'm playing Black now...I still prefer HG at the moment. It might be because I started playing HG after couple years of not playing pokemon at all(new game=exciting), while I started playing Black right after playing HG a lot(new game=more of the same, but different).
Strangely, while playing Black, I keep getting the urge to play Red again, even though I just played it :/ It'd be cool to play the newer games in a retro format, I think.