I'll say this
PS2 - Best is GOW 2
PSP - Best is GOW Ghost of Sparta
PS3 - GOW Ascension. Overall one can argue that GOW 3 is better and I can understand why. It had a better story and it was more epic since it was the final chapter, but I have much more fun and challenge with Ascension.
Playstation = The Beast from the East
Sony + Nintendo = WIN! PS3 + PSV + PS4 + Wii U + 3DS