Yellow, on release day (even though it was only a few days before my birthday!). I was pretty much bed-bound that entire year, and played obsessively. Pikachu, Haunter, Kangaskahn, Dodrio, Dragonite, Articuno. Kangaskahn and Dodrio are still about lv. 30 - 40ish, as they dropped off usefulness towards the end, but I still kept them with me. They eventually went to Gold, and in a mad rush to save my entire pre-2006 collection from battery death, made it to a permanent home on my PC through a ritual using a doohick obtained from the bowels of the internet.
Today, their PokéSav 'clones' languish in a box on diamond due to now being utterly out-classed. And the original Gold .Sav backed up on three harddrives, two phones and an R4.
*modified for typo (ye gods I hate them!)