It is always difficult and dangerous to attempt to list sins according to their degree of seriousness. In one sense, all sins are equal in that they all separate us from God. The Bible's statement, "For the wages of sin is death ..." (Romans 6:23), applies to all sin, whether in thought, word, or deed.
At the same time, it seems obvious that some sins are worse than others in both motivation and effects, and should be judged accordingly. Stealing a loaf of bread is vastly different than exterminating a million people. Sins may also differ at their root.
Theologians have sought for centuries to determine what the essence of sin is. Some have chosen sensuality, others selfishness, and still others pride or unbelief. In the Old Testament, God applied different penalties to different sins, suggesting variations in the seriousness of some sins. A thief paid restitution; an occult practitioner was cut off from Israel; one who committed adultery or a homosexual act or cursed his parents was put to death (see Exodus, chapter 22 and Leviticus, chapter 20).
In the New Testament Jesus said it would be more bearable on the day of judgment for Sodom than for Capernaum because of Capernaum's unbelief and refusal to repent after witnessing His miracles (Matthew 11:23-24). The sins of Sodom were identified in Ezekiel 16:21 as arrogance, gluttony, indifference to the poor and needy, haughtiness, and "detestable things."
When Jesus spoke of his second coming and judgment, he warned that among those deserving punishment some would "be beaten with many blows" and others "with few blows" (Luke 12:47-48). He also reserved His most fierce denunciations for the pride and unbelief of the religious leaders, not the sexually immoral (Matthew 23:13-36).
However, remember that whether our sins are relatively small or great, they will place us in hell apart from God's grace. The good news is that Jesus paid the penalty for our sins and the sins of the whole world at the Cross. If we will repent and turn to Jesus in faith, our sins will be forgiven, and we will receive the gift of eternal life.