I'm pretty sure it was GTA 1 or 2. I never could get used to the top down view. What I remember most was a mission where I believe I was supposed to pick up a girl/wife and I had to hurry. I couldn't find her right away, turned a corner quick and ran over people including her. I then got a beeper message that someone wasn't happy with me and id better be on the lookout.... something to that effect.
But I bought GTA 3 at random. It has just come out and I knew nothing about it really, the gameplay images on the back of the case looked interesting if I recall right. Took it home and was hooked. If they followed age laws back then, I wouldn't have been able to buy it lol.
After Vice City and San Andreas though, my interest has become less and less. Not interested in 6 until it's on sale and on PC I think.