As a Christian, I believe that the most successful life is the one that has stored up the most treasure in heaven, eternal reward, which can never be lost to thieves or decay. Any man, rich or poor, slave or free, can serve God with heroic virtue. And so eternal glory is freely offered to all who seek it. The more you serve God, the more God will reward you with a greater degree of sharing in His divine life in eternity. But even the least in heaven lives in the unimaginable bliss of God. In the same way, every man who knowingly does evil and rejects God, stores up for himself a greater measure of wrath in judgment with every sin.
"Do not store up for yourselves treasures on earth, where moth and rust[
a] consume and where thieves break in and steal; but store up for yourselves treasures in heaven, where neither moth nor rust[
b] consumes and where thieves do not break in and steal. For where your treasure is, there your heart will be also." (Matthew 6:19-21)
"But by your hard and impenitent heart you are storing up wrath for yourself on the day of wrath when God's righteous judgment will be revealed. For he will render to every man according to his works: to those who by patience in well-doing seek for glory and honor and immortality, he will give eternal life; but for those who are factious and do not obey the truth, but obey wickedness, there will be wrath and fury." (Romans 2:5-8)
Edit:
And so the greatest man is not the most handsome, the most strong, the most wealthy, the most famous, etc. Those are merely accidents of one's birth, or fleeting honors and possessions, all destined to fade away into nothing. The man who is most like God, the most holy, the most good, the most loving, he is the greatest man. And so men such as that will have the greatest reward and therefore have lived the greatest and most successful lives.