Who is God's greatest masterpiece?

Answer 1

One Perspective:

The Most Blessed Virgin Mary is God's Greatest Masterpiece. He would never chose an inferior woman to be His Mother. He would never chose a Jesebel. He chose the greatest and holiest of all His creatures, to come into Her womb. "And the Word was made Flesh, and dwelt amongst us." From the Angelus Domini, said daily at Noon, and Six. See book by same title online.

Another Perspective:

The question presupposes that the "masterpiece" is a person by asking "Who," so let the answer go to that.

And God said, Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth. (Genesis 1:26)

Quite obviously, the entire human race fits the description of God's greatest masterpiece. Two very clear reasons:

1. "Let us make man in our image, after out likeness." -- If God did not perceive Man (all humans) to be his greatest achievement, why else would he have given man this gift?
2. ...and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth." -- In essence, God gave Man the keys to the kingdom.

Juxtaposed to this throughout scripture, God gave Man the Freedom to choose. The only other beings of Creation who may or may not have received this were angels, essentially Lucifer/Satan (make your own determinations) and those who may or may not follow or be manipulated by him; but, that's a different discussion.

Answer 2

People are Gods masterpiece of creation.