Also gonna go with HeartGold and SoulSilver. Black and White are amazing and I love them, but before they came out Gen II was my favorite, and HeartGold and SoulSilver just took it and gave it life for the younger players. It was amazing. Plus, over the course of my entire life, Houndoom became my favorite pokémon and that was introduced in the original GSC.
The one thing that makes me sad about HGSS is that there weren't any Contests -- but I'm pretty sure everyone else was happy about that, I think I'm the only person who liked those.
I do have to say though, watching four year olds opening their Black and White versions with glee on the release day was such a great feeling. And then I felt like an old lady because I had an old Magnemite Burger King toy in it's Pokéball on my hip.