There are lists of different sins in several places in the Bible.
“These six things doth the Lord hate: yea, seven are an abomination unto him: A proud look, a lying tongue, and hands that shed innocent blood, An heart that deviseth wicked imaginations, feet that be swift in running to mischief, A false witness that speaketh lies, and he that soweth discord among brethren.” Proverbs 6:16-19
Here pride is the worst sin.
In Matthew 15:19 “evil thoughts” is top on the list. In Galatians 5:19, it is adultery. In Mark 7:22, pride and foolishness are at the end. Talking about other people in an unkind way and not obeying parents, Romans 1:29,30.
I said pride is the worst, this is because it keeps many people from coming to God, because they are too proud to confess their sins. But God saves only sinners, not those who think they are good and righteous, Luke 5:32. He can help man only through Christ. To refuse to accept the Lord Jesus Christ as your Lord and Saviour is the sin which cannot be forgiven. It is the result of pride and rebellion against God.
“All unrighteousness is sin: and there is a sin not unto death” (1 John 5:17). Pride is a sin unto death, on the same level of blasphemy against the Holy Ghost. There isn’t much you can do for a proud person/believer, “….God resisteth the proud, and giveth grace to the humble.” 1 Peter 5:5.
“Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men.” Matthew 12:31
“If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it.” 1 John 5:16
Pride is a sin unto death. Hear this, “For, behold, the day cometh, that shall burn as an oven; and all the proud, yea, and all that do wickedly, shall be stubble: and the day that cometh shall burn them up, saith the Lord of hosts, that it shall leave them neither root nor branch.” Malachi 4:1