Having consulted Garrigou-Lagrange (the "Sacred Monster" of strict Thomism), I think it useful to again mention Aquinas' principle of predilection: "Since God's love is the cause of goodness in things, no one thing would be better than another if God did not will greater good for one than for another" (Summa Theologiæ, I, xx, 3).
Note that this principle follows as a corollary from the general thesis that God's love is the cause of goodness in things: for God does not love things because they are good, no; His love is not passive but active, hence if He love a thing, it is made good. This principle applies in every order, natural and supernatural. In regard to things supernatural, we have the Apostle's rhetorical question - "What hast thou that thou hast not received?" (I Cor. iv, 7).