Pikachu hasn’t been around in a while, but he definitely hasn’t lost his edge. Pikachu is still one of the fastest Pokemon alive and his Volt Tackle packs a punch. Greninja would not be able to endure that kind of power. Greninja is also very skilled and he has a large array of abilities up his sleeve, but the difference in speed between these two fighters is just too great. Pikachu wins.
DReager1.com 
Even though Greninja is faster…
Technically, he may be faster in the games, but the anime Pikachu is just too overpowered. Even before Volt Tackle, Pikachu’s Quick Attack was insanely potent. I don’t believe that Greninja would be able to keep up