Objection 1. It would seem that Moses was not the greatest of the prophets. For a gloss at the beginning of the Psalter says that "David is called the prophet by way of excellence." Therefore Moses was not the greatest of all.
Objection 2. Further, greater miracles were wrought by Josue, who made the sun and moon to stand still (Joshua 10:12-14), and by Isaias, who made the sun to turn back (Isaiah 38:8), than by Moses, who divided the Red Sea (Exodus 14:21). On like manner greater miracles were wrought by Elias, of whom it is written (Sirach 48:4-5): "Who can glory like to thee? Who raisedst up a dead man from below." Therefore Moses was not the greatest of the prophets.
Objection 3. Further, it is written (Matthew 11:11) that "there hath not risen, among them that are born of women, a greater than John the Baptist." Therefore Moses was not greater than all the prophets.
On the contrary, It is written (Deuteronomy 34:10): "There arose no more a prophet in Israel like unto Moses."
I answer that, Although in some respect one or other of the prophets was greater than Moses, yet Moses was simply the greatest of all. For, as stated above (3; 171, 1), in prophecy we may consider not only the knowledge, whether by intellectual or by imaginary vision, but also the announcement and the confirmation by miracles. Accordingly Moses was greater than the other prophets. First, as regards the intellectual vision, since he saw God's very essence, even as Paul in his rapture did, according to Augustine (Gen. ad lit. xii, 27). Hence it is written (Numbers 12:8) that he saw God "plainly and not by riddles." Secondly, as regards the imaginary vision, which he had at his call, as it were, for not only did he hear words, but also saw one speaking to him under the form of God, and this not only while asleep, but even when he was awake. Hence it is written (Exodus 33:11) that "the Lord spoke to Moses face to face, as a man is wont to speak to his friend." Thirdly, as regards the working of miracles which he wrought on a whole nation of unbelievers. Wherefore it is written (Deuteronomy 34:10-11): "There arose no more a prophet in Israel like unto Moses, whom the Lord knew face to face: in all the signs and wonders, which He sent by him, to do in the land of Egypt to Pharaoh, and to all his servants, and to his whole land."
Reply to Objection 1. The prophecy of David approaches near to the vision of Moses, as regards the intellectual vision, because both received a revelation of intelligible and supernatural truth, without any imaginary vision. Yet the vision of Moses was more excellent as regards the knowledge of the Godhead; while David more fully knew and expressed the mysteries of Christ's incarnation.
Reply to Objection 2. These signs of the prophets mentioned were greater as to the substance of the thing done; yet the miracles of Moses were greater as regards the way in which they were done, since they were wrought on a whole people.
Reply to Objection 3. John belongs to the New Testament, whose ministers take precedence even of Moses, since they are spectators of a fuller revelation, as stated in 2 Corinthians 3.
Source: Summa Theologica (New Advent)