Mizuhashi, I agree that IV is great. It brought about my favorite pokemon I've ever raised, Honchkrow. The Previes and Evies in that Gen were also a great addition. So yeah, Gen IV for me. Heck, I even just traded all my stuff up from Platinum to Black and White so I could replay Platinum. :D
Gen IV. Galactic was awesome!!!!! But, like Mizuhashi, Gen III comes in second. XD
Ummm...2 or 3. Those were pretty good. But I like 3 just a TINY bit better.
That's a tough choice, honestly. Perhaps if I thought hard enough I could pick one, but that will be a tight contest. I'll just say I like them all.