Pokemon has had a constant presence in my life literally as far back as I can remember since my earliest memory is playing PMD Blue Rescue Team on my DS.
However my first mainline games were the gen 3 titles which I kinda rotated around since my brother had all 3 but Sapphire was the one that I stuck with years later even if I don't have the cart anymore. However the generation I hold the most affection for gen 4 if the background didn't make it obvious enough.
I grew up with the Sinnoh era and it holds a truly special place in my heart, I have a lot fond memories regarding it. I watched the anime all the time on Citv and those opening songs are burned into my soul. I played the games a lot with my cousins and some strangers in the dentist one time which is one of my favourite interactions I've had related pokemon. One of those guys traded me a Manaphy egg and it was so cool discovering it's existence throught that interaction and it remains my favourite mythical because of it.
Anyways the Sinnoh games themselves appeal to me greatly with it's winter vibes, especially in Platinum, and the great music which I still occasionally leave my ds running just to immerse self in the vibes. My favourite tracks are the Jubilife City, Pokemon Leauge and Route 228 theme. I also really like the ending theme, it makes me feel fuzzy inside. Snowpoint City too, now that I think about it, I really bloody love snow themed areas. Shoutout to the Global Terminal in Platinum, it's theme perfectly encapsulates how it felt using wifi connection on the DS back then.
Beyond Sinnoh, I also really like Gen5, with Black and White 2 fighting for best game with Platinum in my eyes. I like the music of the Unova region too along with the really nice 3d 2d hybrid environments that still look really good. Snivy is also my favourite starter, I knew it from the moment I first saw it back then. Even though it's not that great especially in the sequels I love the regalness of Serperior and I just think it looks cool.
After that came Generations 6 and 7 which I don't enjoy going back to as much but I really like the overall vibes off. The eastern side of Kalos, beyond Laverre Town has some of my favourite places such as Anistar city and Snowbelle city Gen 7. The gen 6 remakes of Ruby and Sapphire are also one of my favourite games in the series. I played Alpha Sapphire a lot and also attempted to dip my toes in competitive at the time even if I didn't understand it until much later. The secret bases of ORAS were also super cool to me, being able to visit others after interacting with them online and making my own was nice.
on the other hand, I love the unique tropical vibe of. It also has some great pokemon designs and music. I really like the Hau'oli city day and night themes plus the Ten Carat hill theme. Those games also had a really good story and gave me some decent trouble near the end with the elite four. One other thing about Gen 7 I'm fond of is period of time when those games were the new ones coming out. You had the gen 1 rereleases and Pokemon Go reviving the pokemon craze a little. It felt nice to be a fan back then with all the stuff going on.
Last thing I wanna talk about is stuff made by fans. Serebii, I started using it during the gen 5 days and it still remains the most reliable source for info for anything pokemon related in my eyes. I enjoyed checking the main page to see if new stuff was revealed and checked the site religously during the lead up to the release of Black and White 2. I played a lot of romhacks too, I'm pretty the first one I touched was Pokemon Snakewood and that certainly was a game of all time. I played a lot of pokemon MMORPGs too. From what I remember I think the ones I frequented were Pokemon Indigo, Pokemon Vortex and Pokemon Lake. I honest don't remember much about them besides playing them after school with friends. Finally there was Pokemon Tower Defense 2, a flash I played a lot. It had a unique story to it but I remember it being sorta comical more than anything.