Here are a couple of points that immediately jump to my mind.
St. Thomas Aquinas was always part of the Church, St. Augustine was a convert who lived a pretty decadent life.
Aquinas was never involved in heresy. Before his conversion, Augustine was deeply involved with Manicheism.
Both wrote books on apologetics. Aquinas wrote the multi-volume Summa Contra Gentiles that was directed principally at those who were not part of any faith or were involved in Northern European and Germanic pagan religions. Augustine wrote City of God which was directed at pagans following the classical Roman and Greek pantheon. He also spoke out strongly, even mockingly, against astrology.
Both had exceptionally impressive intellects which were exceeded only by their waistlines.
Aquinas was a priest. Augustine was ordained a bishop directly, something “demanded” by the people of his city due to his faithfulness, popularity and strong leadership abilities.
Aquinas was a pure academic. Augustine was a “down-in-the-trenches” bishop who happened to be very good at writing.
Aquinas was childless as he was a faithful priest all his life. Augustine had a son with a mistress before his conversion. Both he and his son converted at the same time and his died about 1-1/2 years later.
Aquinas’ mother was a good and faithful woman. His father not so good as he did not want his son to be a priest and actually imprisoned him for over a year and even hired a prostitute to, unsuccessfully, tempt him. Augustine’s mother is a cannonized saint, St. Monica. His father was a pagan who converted but died while still a catechuman.
Both men wrote their books in Latin.
That is about all I can recall from the top of my head.