Given of course we're already talking about a criminal justice system which effectively says to the accused: you're on trial for your life; if we find you guilty we're going to kill you. Given this - and everything that may go with it (concocted or withheld evidence, highly political cases, bungled trials, disparities between the imposition of a death sentence in one case and not in another almost identical one, and so on and so on), does it even matter which method they use? I'd say no, not really. They're all inhumane in principle. The practice is simply another layer of inhumanity, to a greater or lesser degree.
The true significance of the death penalty is as a symbol of man's inability to create a completely peaceful and civilised society. We can blame violent video games and television programmes for the violent crimes that appear in the news every month, but until we abolish a punishment that legally acknowledges violence as a viable means of justice, problems will continue to persist.
Politicised show trials, error-strewn and near-racist courtrooms, mistakes corrected decades after the fact, ethically indefensible overlaps between judicial and medical protocols, ghoulishly botched attempted executions... all these and more are actually fairly typical of the 21st-century death penalty, not rare aberrations.