They are mostly equal in God's eyes, but in my opinion it would be Saint John the baptist or Saint Mary, since they both played a big part in Jesus Christ's life.

There are many Great Saints! One of my favorite is St. Francis of Assisi

“Preach the Gospel at all times and when necessary use words.”

“Start by doing what's necessary; then do what's possible; and suddenly you are doing the impossible.”

“Lord, make me an instrument of your peace; where there is hatred, let me sow love; where there is injury, pardon; where there is doubt, faith; where there is despair, hope; where there is darkness, light; and where there is sadness, joy.”