Yes blasphemy of the Holy Spirit is the worst of sins, which is verbal hatred, slander, misuse, or anything negative toward the Spirit of God. This sin, as said by Jesus Himself, is accountable for no forgiveness and accompanied by eternal hellfire. Among major sin though is Jealousy, Homosexuality, Hate, Murder, worship of another god or thing(money, fame, family, anything that gets more love and attention than God). But after blasphemy of the Holy Spirit, ALL sin can be forgiven no matter how major. But in order for it to be forgiven you must TURN completely away from it, not just once, but for good. It is best to stay in a repentant state.
Perhaps the one sin that is greatest in the Bible is blasphemy, The Word of God says in Mark 12:28-30 " And one of the scribes came, and having heard them reasoning together, and perceiving that he had answered them well, asked him (Jesus), Which is the first commandment of all? And Jesus answered him, The first of all commandments is Hear O Israel; The Lord our God is one Lord: And thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind, and with all thy strength:this is the first commandment.":
God says ascribing partners to Almighty God is the Greatest sin and Blasphemy and it never will it be forgiven. (Obvoiusly people do this without any divine proof.) In any form it is strictly forbidden. All men of God including Jesus preached purest and strict form of monotheism and that is to be followed by all human beings.
