Mary would be great since she always points to her son: "do what ever He tells you". But the Holy Spirit is who is the font of knowledge and understanding.
I shivered a little when you wrote that it would be great to pray to Mary. I just find it repulsive: the idea of praying to a dead, created being.
I don't have a problem asking my live friend to pray for me. But no where does God promise that the dead can hear me.