What was your first anime? When did you started to watch it? How did you become aware of its existence?
Was it the anime that made you an anime fan? (If you consider yourself as such)
How does it rank for you? Would you say you still like it? Would you consider it one of you favourite anime series?
Hard to say for sure but probably Speed Racer. Dragonball Z is definitely the first one I followed consistently. But Speed Racer would have likely been the first I came across.
It would have been playing on Cartoon Network pre-toonami when I was a kid. Back before the US thought there was any difference in Japanese Animation vs US animation.
Spirited Away is what set me to going out of my way for more. But Toonami gave me Gundam Wing, Outlaw Star, .Hack//Sign and Inuyasha while Adult Swim got my Cowboy Bebop, Trigun, Wolfs Rain, etc.
I saw Spirited Away in a theater in the mid 2000s and started downloading stuff left and right.