Isn’t there at least one sin worse than other sins?

Answer:

"Assuredly, I say to you, all sins will be forgiven the sons of men, and whatever blasphemies they may utter; but he who blasphemes against the Holy Spirit never has forgiveness, but is subject to eternal condemnation" (Mark 3:28-29).

In the passage cited, Jesus is discussing the possibility of forgiveness of sins. There is one sin that cannot be forgiven, simply because the sin involves the rejection of the only means to gain forgiveness. See "A Sin Leading to Death" for more details.

All sins that have not been forgiven are punished in the same manner. "But the cowardly, unbelieving, abominable, murderers, sexually immoral, sorcerers, idolaters, and all liars shall have their part in the lake which burns with fire and brimstone, which is the second death" (Revelation 21:8). Most people don't consider lying nearly as bad as committing a murder; yet, the end result of both sins is exactly the same. Hence, a person who blasphemes against the Holy Spirit, refuses to repent, and, thus, cannot gain forgiveness of his sin, will receive the same punishment as a murderer or a liar who could have been forgiven but never repented of his sin.

Jesus spoke of this: "There were present at that season some who told Him about the Galileans whose blood Pilate had mingled with their sacrifices. And Jesus answered and said to them, "Do you suppose that these Galileans were worse sinners than all other Galileans, because they suffered such things? I tell you, no; but unless you repent you will all likewise perish. Or those eighteen on whom the tower in Siloam fell and killed them, do you think that they were worse sinners than all other men who dwelt in Jerusalem? I tell you, no; but unless you repent you will all likewise perish"" (Luke 13:1-5). Unless a person repents of his sins, it doesn't matter what sin he is guilty of committing, he will face the same punishment reserved for every other sinner.

"For if God did not spare the angels who sinned, but cast them down to hell and delivered them into chains of darkness, to be reserved for judgment; and did not spare the ancient world, but saved Noah, one of eight people, a preacher of righteousness, bringing in the flood on the world of the ungodly; and turning the cities of Sodom and Gomorrah into ashes, condemned them to destruction, making them an example to those who afterward would live ungodly; and delivered righteous Lot, who was oppressed by the filthy conduct of the wicked (for that righteous man, dwelling among them, tormented his righteous soul from day to day by seeing and hearing their lawless deeds) -- then the Lord knows how to deliver the godly out of temptations and to reserve the unjust under punishment for the day of judgment" (I Peter 2:4-9).