If a character is attached to the unit, use the unit's suppression score. Robert the Reaver with his steam armor of awesomeness is still in danger when surrounded by a bunch of greenhorns.
If a character has a suppression value of more than one, then just place a die by the knocked-over figure if he's acting a his own unit to denote how many suppressions he has.
In any case, if there are more unsaved hits from a volley of fire than there are figures in the unit, the unit is destroyed. This applies to single-model units like characters on their own.