Objection 1. It would seem that the angels are not more to the image of God than man is. For Augustine says in a sermon de Imagine xliii (de verbis Apost. xxvii) that God granted to no other creature besides man to be to His image. Therefore it is not true to say that the angels are more than man to the image of God.
Objection 2. Further, according to Augustine (QQ. 83, qu. 51), "man is so much to God's image that God did not make any creature to be between Him and man: and therefore nothing is more akin to Him." But a creature is called God's image so far as it is akin to God. Therefore the angels are not more to the image of God than man.
Objection 3. Further, a creature is said to be to God's image so far as it is of an intellectual nature. But the intellectual nature does not admit of intensity or remissness; for it is not an accidental thing, since it is a substance. Therefore the angels are not more to the image of God than man.
On the contrary, Gregory says (Hom. in Evang. xxxiv): "The angel is called a "seal of resemblance" [Ezekiel 28:12 because in him the resemblance of the Divine image is wrought with greater expression."
I answer that, We may speak of God's image in two ways.
First, we may consider in it that in which the image chiefly consists, that is, the intellectual nature. Thus the image of God is more perfect in the angels than in man, because their intellectual nature is more perfect, as is clear from what has been said (58, 3; 79, 8).
Secondly, we may consider the image of God in man as regards its accidental qualities, so far as to observe in man a certain imitation of God, consisting in the fact that man proceeds from man, as God from God; and also in the fact that the whole human soul is in the whole body, as God from God; and also in the fact that the whole human soul is in the whole body, and again, in every part, as God is in regard to the whole world. In these and the like things the image of God is more perfect in man than it is in the angels. But these do not of themselves belong to the nature of the Divine image in man, unless we presuppose the first likeness, which is in the intellectual nature; otherwise even brute animals would be to God's image. Therefore, as in their intellectual nature, the angels are more to the image of God than man is, we must grant that, absolutely speaking, the angels are more to the image of God than man is, but that in some respects man is more like to God.
Reply to Objection 1. Augustine excludes the inferior creatures bereft of reason from the image of God; but not the angels.
Reply to Objection 2. As fire is said to be specifically the most subtle of bodies, while, nevertheless, one kind of fire is more subtle than another; so we say that nothing is more like to God than the human soul in its generic and intellectual nature, because as Augustine had said previously, "things which have knowledge, are so near to Him in likeness that of all creatures none are nearer." Wherefore this does not mean that the angels are not more to God's image.
Reply to Objection 3. When we say that substance does not admit of more or less, we do not mean that one species of substance is not more perfect than another; but that one and the same individual does not participate in its specific nature at one time more than at another; nor do we mean that a species of substance is shared among different individuals in a greater or lesser degree.
Source: Summa Theologica (New Advent)