This shouldn't be too tough. Tintoretto's Last Supper is more dynamic and dramatic but Christ is in the center as in Leonardo's Last Supper. The spiritual is blatant in Tintoretto's painting too, but in Leonardo's version, not even Christ has a halo. You can also talk alot about the differences in how the two artists make balance in the painting and how they create depth. In Leonardo's work, one of the things he does to create balance is grouping the apostles into groups of three. You can compare and contrast their styles, their techniques, and their goals in making the piece.
