Then what determines which gets which?
The will of God.
From Augustine:
Chapter 36.--God Chose the Righteous; Not Those Whom He Foresaw as Being of Themselves, But Those Whom He Predestinated for the Purpose of Making So.
....Let us, then, look into the words of the apostle and see whether He chose us before the foundation of the world because we were going to be holy and immaculate, or in order that we might be so. “Blessed,” says he, “be the God and Father of our Lord Jesus Christ, who hath blessed us in all spiritual blessing in the heavens in Christ; even as He hath chosen us in Himself before the foundation of the world, that we should be holy and unspotted.” [Eph. i. 3] Not, then, because we were to be so, but that we might be so. Assuredly it is certain,--assuredly it is manifest. Certainly we were to be such for the reason that He has chosen us, predestinating us to be such by His grace. Therefore “He blessed us with spiritual blessing in the heavens in Christ Jesus, even as He chose us in Him before the foundation of the world, that we should be holy and immaculate in His sight, in order that we might not in so great a benefit of grace glory concerning the good pleasure of our will. “In which,” says he, “He hath shown us favour in His beloved Son,”--in which, certainly, His own will, He hath shown us favour. Thus, it is said, He hath shown us grace by grace, even as it is said, He has made us righteous by righteousness. “In whom,” he says, “we have redemption through His blood, the forgiveness of sins, according to the riches of His grace, which has abounded to us in all wisdom and prudence; that he might show to us the mystery of His will, according to His good pleasure.” In this mystery of His will, He placed the riches of His grace, according to His good pleasure, not according to ours, which could not possibly be good unless He Himself, according to His own good pleasure, should aid it to become so. But when he had said, “According to His good pleasure,” he added, “which He purposed in Him,” that is, in His beloved Son, “in the dispensation of the fulness of times to restore all things in Christ, which are in heaven, and which are in earth, in Him: in whom also we too have obtained a lot, being predestinated according to His purpose who worketh all things according to the counsel of His will; that we should be to the praise of His glory.”