Well, I started out with a Nano Kitty. I raised mine to be 33 years old, the only problem was how easy they are to reset, all you had to do was press the first and last button (i think it was Circle and Square) for two seconds and it would start over. A girl in my ballet class did that as soon as i told her not to. I cried. It was horrific, so i started playing with virtual pets that weren't so easy to reset, like digimon and a pokemon pikachu. And then I think my nano kitty stopped working, or i lost it. i can't remember.
But I like the Digimon more, so I suggest throwing that into the contest as well, because they are awesome. I have a V1. Its uber.
Therefore, I vote for the tamagotchi. I'm 19, and I just got my first one a week and a half ago. V4.5 on sale at a KB toystore closing out. Only $7!!!!
lets see a cat...a cool awesome creature...online tama stuff...weird shape...egg shape... TAMA! 
