They're both amazing pins. And this comparison is great for me, because they're literally side by side and the only two pins I have right now.
GnR gets more play.
That's not to say that GZ is a slouch or a bad game, it's amazing. But I find myself playing GnR more. But they're quite different games, so I'm not sure they can or should even be compared if you're making a purchasing decision of one or the other.