The Ramban in his introduction to Iyov tell us that one moment in Gehinom is more painful than all the tzoros of Iyov (quoted by the Chafetz Chaim in one of his seforim).
R’ Levy Yitzchak of berditzev is purported to have said that he’s not afraid of Gehinom because if if it’s rotzon Hashem for him to be there then there’s no better Gan Eden he could experience than fulfilling Hashem’s rotzon.