My first pokemon game was Yellow, but I really got into it proper when I was a little older and Gold and Silver came out, since me and my best mate could play it all weekend.
My favorite has to be Crystal. It had all the things that I loved from Gold and Silver (eg. best looking pokemon, best starters, best cities, IMO of course) plus it had some new little quests which just added to the longevity to the game.
Also, most people got something shitty from the pokemon breeder in Goldenrod City, y'know what I got from that egg? I FUCKING MAGBY, that's what!
You can imagine how off the wall I went when I got that, at age 12.