“I’m for the most painless death possible.”
Not me, I have a strong vindictive streak.
Most of those monsters caused their victims a lot of pain before they killed them. Let the punishment fit the crime I say.
Painless punishment is no punishment at all.
You’re sending them to meet their maker. Nothing you can do is going to be a more just punishment than what He does to them.
Any additional pain you cause is just delaying their final judgement, and is more about you than anyone else. If the death penalty isn’t a deterrent to others, a painful death penalty isn’t going to be either.