A rope is none of these things but is damn effective.
The constitution doesn’t guarantee a painless execution.
Ropes can break, decapitate, or not break the neck. So I would have to say that they are mostly effective. However, when they don’t work, it’s often put out by the media as torture. This then in turn leads to lawyers, lawsuits, “pain and suffering” BS. So, mostly effective but not lawyer friendly.
With Nitrogen Asphyxiation, put on a mask, 1.1 atmospheres of 99% nitrogen gas, and monitor till the brain waves go flat. The condemned passes out painlessly from a lack of oxygen. No “pain and suffering”, no drugs, no failures, no blood, no gore, no lawyers, no lawsuits. Just a nice and tidy execution. Rack’em, Stack’em and set up for the next one.