I really want to say Pokémon because it was part of childhood and I grew up with it. But Yu-Gi-Oh ******* so hard, I was addicted to it and at that point I totally paid Pokémon dust. Yu-Go-Oh's series with Yugi were perfection, so cool.
Yugioh was fun when I was a kid, I was a huge fan of the card game and went to local tournaments and such, but I voted Pokemon because I think it's had a bigger impact overall. I've grown out of YugiOh, but Pokemon is still as cool as ever!