[AlexandrB]

There's an effect where the visceral emotional response to an execution method overrides the actual cruelty of the act. Lethal injection, for example, is probably horribly painful for at least some of those that experience it[1] but it looks humane to observers. Meanwhile, the trusty guillotine would be my chosen way to go since it's nearly instant.

[1] https://eji.org/news/lethal-injections-cause-suffocation-and...

[rtkwe]

Nitrogen suffocation any day of the week in my opinion. Your brain lives long enough after the guillotine you definitely have time to feel the pain of the cut while your brain can't even register the hypoxic effects from N2 suffocation.

[tantalor]

More at https://en.wikipedia.org/wiki/Inert_gas_asphyxiation

Good demo here: https://youtu.be/kUfF2MTnqAw?si=Fi3590AiHdTBW3r8&t=329

[AlecSchueler]

There's plenty of time to feel excruciating panic walking up to bend over and lose your head. The cut itself may be instantaneous but that's not really all there is to it.