Pokemon will always be like.. a subtle obsession of mine. I say subtle because I go through phases where I don't really think about it or play the games.. but I've had a game for every generation of main line games to come out, and I've played a fair share of spin off games.
First game was Blue! Though I think I started playing it a bit late as I remember gold/silver coming out not too long after I first played. My favorite would probably be Ruby or Pearl, though honestly it's hard to pick. I just have a bad habit of playing and never actually beating most of the games lol.
I was addicted to wonder trading for a long time.. I would breed full boxes of somewhat hard to get pokemon, name them, breed egg moves etc and sit there and just trade out a whole box all at once.
My favorite pokemon is basically impossible to answer so I wont even try to pick just one lol. I have a soft spot for meowth (all of them) and haunter, though.
I'm SUPER excited for Legends: Arceus! I will definitely be getting it. The Diamond/Pearl remakes I might skip this time though as I really don't have the money to be spending on games I wont play fully, especially since it's going to be more expensive as a Switch game. @_@
I really enjoy a lot of the spin off games.. I wish they would come out with another pokemon Ranger title but idk how well it would work on the switch without a stylus.. still, those were fun games.
Now I just spend most of my pokemon-obsession-time playing in an ARPG on deviantart and drawing and breeding them haha!