Look, whilst I'm not against capital punishment as a matter of principle, because we have such a very imperfect system of justice, I would rather life imprisonment instead. That way he have a chance of correcting mistakes and miscarriages of justice.
But having decided to execute someone, the state should carry it out in as a quick and painless a method possible (if there is such a thing). Just Shoot the guy or use any method with results in instant death (head chopped off?). This fixation with experimental drugs and electrocution and suffocation and all similar methods which prolong the death spasms are sick and should stop immediately. People who advocate these methods should be stripped of all authority in these matters and sent to the nearest shrink.
The state must never torture a citizen to death. That's not what the state exists for and that is too disturbing a precedent to set. And those who advocate death by prolonged torture should be ejected from the state execution bodies.