I'm late to the party here. But it is a very interesting question.
I would have to say that crucifixion in and of itself is probably not the worst form of torture death although it is certainly among the top.. I don't think we will know what is the worst kind of death penalty..no one has come back to tell us.
The worst kind of suffering is that which a loving parent endures at the hands of children who hate and want him dead. Please phil, start looking at the gospel this way.
However that's not really the point. The point is God appointed his son to die.
God appointed his Son to endure the sins being committed against him and in spite of this, continue loving those who hated him,
love is long-suffering 1Cor.13:4
consider him that endured such contradiction of sinners against himself Heb.12:3
Crucifixion was the form Rome used for its so called detestable law breakers. The fact that God the Father poured out His wrath for all those saved past,present and future upon his son on the cross tells us that it is a far greater punishment than anyone man will receive. And that is simply that each person will only receive his own punishment not for the many like our Lord Jesus.
God did not pour out his wrath on his Son. Sinners poured their wrath out on Gods Son,
They hated me without a cause Jn.15:25
1 John 2:2
He is the propitiation for our sins, and not for ours only but also for the sins of the whole world.
Jesus turned his wrath away from people who sinned against him.
1 Thess 5:9
For God has not destined us for wrath, but to obtain salvation through our Lord Jesus Christ,
Because Christ turned the other cheek, instead of destroying the ungodly who sinned against him.
Romans 5:8-9
But God shows his love for us in that while we were still sinners, Christ died for us. Since, therefore, we have now been justified by his blood, much more shall we be saved by him from the wrath of God.
Justified by his blood, that is his life.
Hebrews 2:17
Therefore he had to be made like his brothers in every respect, so that he might become a merciful and faithful high priest in the service of God, to make propitiation for the sins of the people.
Read the next verse.
So the point is. no matter how bad hell is, you will only receive your own punishment. Not that of other on top of your own.
Romans 2:5
But because of 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
The point is, anyone who has not repented of sinning against God will face the wrath of God,
But here is something to remember and cherish:
1 Peter 3:18
For Christ also suffered once for sins, the righteous for the unrighteous, that he might bring us to God, being put to death in the flesh but made alive in the spirit,
What does Peter mean by "also"? "Also suffered"? Read the verse before it.