Hard to say but I will say that I really enjoyed the MMZ series. I think there was a lot of flexibility MMZ version of Zero. As for X, he never fought in the zero series so it would be hard to measure his power. In the zero series, Zero had a better balance in using both his buster and sword along with using other weapons just as he did in X7 and X8. I would have to say that MMZ Zero is better. That was literally his series and time to shine. X needed to take a backseat for he was taking his place back in the X series. As the X series progress, Zero became more and more alive and it helped him transition to MMZ. After MMZ, going into the ZX series, in the fusions MMZ stands as the dominant of all of the fusions. In ZXA his form is the most powerful form to have.