Which best describes the projectile motion of the marble as it leaves the table at the two different speeds?

Marble with higher speed.

Explanation:

When a marble is thrown with low speed, then it covers less horizontal distance but the marble with higher speed covers more horizontal distance though they both travells through same height from table (i. e. vertical distance).

Since both horizontal and vertical distances are responsible for projectile motion, marble with higher speed describes the motion of projectile more effectively.