I would say PS2, but also combined with the PSone, PS1 was my first console but a lot of the PS1 games I have played were bought when I already had a PS2. In fact the first two games I bought when I got a PS2 were FFX and Hogs of War (Psone). Because I'm not a graphics whore I still look on PS1 as acceptable, even FFVI which I actually look on as a good-looking game despite the fact that even my dad (who has never played a video game in his life) mocked its graphics.
Although I am sometimes astounded by the good graphics on games on the current-gen and even on PS2 I see them as an bonus, not the main feature.
When I soon get some RAM for my incredibly slow PC I can see myself falling in love with all those games that have just frustrated me because they are so pathetically lagged.
The N64 also has a place in my heart, I only got one recently but I would love it even if the only game on it was ocarina of time.
Lately the DS has gained my love by saving me on many a boring holiday.
However the console which I have been most hopelessly addicted to is the GBC.
I spent months on it playing Pkmn Red/Gold, the Zelda games on it, Super Mario Brothers Deluxe.