Heres a nerdy rundown
painful would have to be springlock failure, for those who don't know, when you get springlocked the death will be slow and painful and your lungs will be filled up with blood until you drown in your own blood, plus all the iron bars used to hold endoskeleton in place will be forced into you, most likely holding around your skeletal structure (some of this is explained in the first book of the silver eyes trilogy) its also explained in the games that it will force your eyes out however i'm not sure if that just implies to the normal suits. but if we are talking about visual effects? yeah torture freddy would be more brutal.