If we live on one of the most unrighteous worlds that our Father made, why did He choose this one on which to have his son born? Also, were we more inferior spirits in our first estate than inhabitants of other worlds when we lived with the father so were sentenced to come this more wicked world?
We do not live on one of the most unrighteous worlds that our Father made, we live on the very most wicked world in all the universe! The Lord said to Enoch on one occasion—
Wherefore, I can stretch forth mine hands and hold all the creations which I have made; and mine eye can pierce them also, and among all the workmanship of mine hands there has not been so great wickedness as among thy brethren. (Moses 7:36)
The Savior came here to work out the great atonement, specifically because it was the most wicked of all worlds—
He [the Savior] that ascended up on high, as also he descended below all things, in that he comprehended all things, that he might be in all and through all things, the light of truth.(D&C 88:6)
The above scripture says that he descended below all things, not just all things on this one earth.
However, the Savior has determined to save this world, to make it a celestial kingdom, His own residence. In order to bring that about, it is my opinion that He must send here also the most righteous spirits in the universe to offset that wickedness. This could be one application of the scripture—
For it must needs be, that there is an opposition in all things. If not so, my first-born in the wilderness, righteousness could not be brought to pass, neither wickedness, neither holiness nor misery, neither good nor bad. Wherefore, all things must needs be a compound in one; wherefore, if it should be one body it must needs remain as dead, having no life neither death, nor corruption nor incorruption, happiness nor misery, neither sense nor insensibility. (2 Nephi 2:11)
So, depending on how you follow the dictates of the Savior in complying with all the principles and ordinances of the Gospel of Jesus Christ, you could be among the most righteous in the universe. One of the ordinances in the holy temple seals upon the recipients all the blessings of Abraham, Isaac and Jacob. Those blessings are far reaching beyond our imagination. An insight to such blessings is found in the book of Abraham 3:22-23—
Now the Lord had shown unto me, Abraham, the intelligences that were organized before the world was; and among all these there were many of the noble and great ones;
And God saw these souls that they were good, and he stood in the midst of them, and he said: These I will make my rulers; for he stood among those that were spirits, and he saw that they were good; and he said unto me: Abraham, thou art one of them; thou wast chosen before thou wast born.
So Abraham was one of those who were the noble and great children of our Father in Heaven and from among the Father will choose those to be rulers in His kingdom. You could also be one of them!