For me:
1. God of War 2
2. God of War 3 (epic boss fights helped it, cause the gameplay part going through Olympus all the time and the art style were worse than 2 & Ascension)
3. God of War Ascension
4. God of War
Didn't play the PSP ones, maybe on the Vita.
Funnily enough the order I played them in is GoW3>GoW2>GoW:A>GoW(started it before Ascension but didn't finish).
That's the reason I don't care about the supposedly progressively worse story in each game, cause well Iplayed the franchise backwards 
They all have an amazing gameplay though, maybe my favourite gameplay in a game ever. That's why I hope we'll see another GoW game on the PS4 asap. And the fact that Cory Barlog (GoW2) is back on board again, makes me very excited!
So it is happening...PS4 preorder.
Greatness Awaits!
