Totally depends on the decision that needs to be made.
Most of the time I go with my what my head tells me to do, because usually it's the smartest thing to do.
Sometimes, my gut instinct is very, very strong. And in those situations, I will go with it.
And every once in a while I will go with my heart. Why? Because, sometimes you just have to do something that makes you happy, even when you know it isn't the smartest thing to do.
Usually the best (and easiest) decisons made are ones where your head, heart and gut are all saying the same thing.