The extraordinary thing about Jesus' suffering is not so much its physical intensity, but the fact that He, the Second Person of the Trinity, deigned to suffer. He did not have to, but he specifically wished to save us by enduring suffering.
We should also keep in mind that Jesus, being God, had (and has) perfect knowledge of all the sins committed in the past, present, and future, and His suffering was made infinitely worse by that knowledge. It was this moral suffering, it seems, that caused Him to sweat blood during the Agony in the Garden:
And being in an agony he prayed more earnestly; and his sweat became like great drops of blood falling down to the ground (Lk 22:34).
Finally, by suffering to expiate our sins, He also entered into perfect solidarity with those who suffer in the world, giving them hope (if they live it united with Him, at least), and a meaning to their suffering.
EDIT: St. Thomas Aquinas supports the view that Jesus' suffering was the greatest both physically and morally. I quote below a portion of his responsum to Summa Theologiae, IIIa Pars, q. 46, a. 6:
[T]here was true and sensible pain in the suffering Christ, which is caused by something hurtful to the body: also, there was internal pain, which is caused from the apprehension of something hurtful, and this is termed “sadness.” And in Christ each of these was the greatest in this present life.
The magnitude of His suffering may be considered, secondly, from the susceptibility of the sufferer as to both soul and body. For His body was endowed with a most perfect constitution, since it was fashioned miraculously by the operation of the Holy Ghost.... And, consequently, Christ's sense of touch, the sensitiveness of which is the reason for our feeling pain, was most acute. His soul likewise, from its interior powers, apprehended most vehemently all the causes of sadness.
In other words, because Jesus was perfect man as well as perfect God, he was actually more sensitive to physical and moral sufferings than we would be.
It is possible to hold different opinions about this topic (as long as uniqueness of the act of Redemption is maintained), but Thomas' position is well worth considering.