Both very cool options. Personally my fav of those three is God of War II, I do like Ninja Gaiden Sigma better than the first God of War though.
You can't lose! I think you can beat God of War faster, plus it's easier, not sure if that'll influence your decision.
I'll say... play Ninja Gaiden Sigma first. Then, since Ninja Gaiden II isn't very good anyway, you got time to rock some God of War trilogy action.
--
One Piece: Pirates with style!
-= Metal Gear Solid: Tactical Espionage Action =-