If you don't know what a generation of Pokémon is, then I can somewhat explain it. A generation of Pokémon is, well, the easiest way to put it is each series of three or more games. For example, Ruby, Sapphire, and Emerald make up the third generation, because all games are connected to each other. All of the new Pokémon, Items, Characters, etc. also count in a generation.
So, Gen. I is Red, Blue, and Yellow.
Gen. II is Gold, Silver, and Crystal.
Gen. III is Ruby, Sapphire, and Emerald. FireRed and LeafGreen are also included in Gen. III.
Gen. VI is Diamond, Pearl, and Platinum. HeartGold and SoulSilver are also considered Gen. IV.
My favorite Generation is Gen. II. Let's face it, Gold and Silver were the best Pokémon games period. That's why the hype for their remakes is still going strong.
And believe me, I hyped Gold and Silver like nothing else. I even found a guide that somebody imported the games and made. So I knew everything about Gold before getting it, and it still lived up to my hype.
Very few games have lived up to my hype, and almost every one of them that has, but Gold/Silver/Crystal I didn't know much about beforehand.
They were clearly the best games out of the whole series. Awesome music. Full color graphics. Day and night system. Week system. More Pokemon. (back when there weren't already too many. XD) The ability to go back to Kanto after the main Johto journey.
And lastly, the best part, Gold/Silver/Crystal really only added onto Red/Blue/Yellow. They didn't take away any important features, they kept them all and just added onto it.
It's sequels like that, that live up to my hype. Sequels that don't remove things that made the originals so great. Sequels that actually top the originals.
It's a huge shame that Ruby/Sapphire/Emerald did take away features and ruined it.
Oh, and second generation allowed the option to be a female trainer! Yay! I was so sick of having to be the male trainer.
Easily Generation RSE, among the awesomesauce that is the OST (I've always mentioned this characteristic first throughout the years xD), the fact they've put a good chunk of water routes in the region among with the overall composition of it all (landscapes range from mountains to beaches, cities incorporated in trees, sea, etc.)
Although biased, many of my favorite Poogeymanz were churned out during this gen, same with gym leaders.
Aaaand lastly I should mention contests which were much more straight forward and less gay back in the days.
My favourite generation is Gen 2. But that will soon change with the release of Pokemon Heart Gold & Soul Silver; they'll make me love the 4th Gen a whole lot more