god of war is a very linear game, it's a must play game because of the amazing scale of it, but it's short and there is no multiplayer or real replay value (unless you want to test yourself on higher difficulty or need to get all achievements)
heavy rain has the advantage of having multiple ways the game can play it, even if it still a short game.
IF I were you i'd get a game with a bit more length and replability, and wait until heavy rain becomes cheaper (i think it's value will go down fast)
if it's a choice between those 2 get god of war and wait till heavy rain gets cheaper.