Shastras are spiritual scriptures, which are results of spiritual analysis. They are a logical analysis of the Ultimate Truth. They give you intellectual clarity, understanding and confidence about the Ultimate Truth.
Stotras are outpourings of love and devotion towards the Divine. They create an emotional attachment to the Divine. While shastras talks of the Ultimate Truth, stotras are the expression of the experience of the Ultimate Truth.
Sutras are the bridge between these two. They are the fulfillment of these two. They are techniques that take put you directly into the experience of the Ultimate Truth. They are the only solutions available to us.