Thoughts on methods of capital punishment

Hangings, firing squads, and the guillotine are viewed as horrible methods of execution from our less civilized past. The electric chair is going that direction. Lethal injection is the new 'sanitary' way of executing. But who is it really sanitary for, the executed criminal or the living? All forms of execution can be painful for the executed criminal if not properly applied, so let's assume that all of these methods are going to be properly applied. Our modern, humane methods of execution actually take longer than the older, disreputed methods. In a proper hanging, guillotine beheading, or firing squad exectuion, death is instantaneous. In the electric chair or a lethal injection, we may feel more civilized, but the death is actually prolonged and the executed must experience dying. Is either really improvement upon the previous three, or are they just ways to assuage our guilt and to keep our hands physically cleaner?