Executing all death row prisoners tomorrow would not do anything to ease overcrowding, as there are less than 3000 people sentenced to death, but over 3 million people in jail. Life without parole is cheaper, reversible when the conviction is in error, less legally time consuming and brings a much quicker resolution to the victims families, as opposed to years of appeals and court appearances.
The death penalty if carried out expeditiously would cut down on prison overcrowding and the cost of housing prisoners. In addition the quick execution (pun kind of intended) of the death penalty might work as a deterrent while bringing faster closure to victim families. On the other hand, the death penalty is permanent, and some convicted criminals have been proven innocent. Some families might think this was too quick of an end to the person who victimized them or their loved ones.
I am not sure that I could choose which is a worse sentence, death or life without parole. I think that most people who commit the types of violent crimes that require either sentence would probably not be as bothered by a life sentence as we might think. For some life in prison may not be that much of a punishment anymore.
The death penalty is arguably a less harsh punishment than a life term without parole. It can be argued that a person who knows that they have to spend the rest of their lives imprisoned is worse off than a person who knows that they will be executed after a few years in prison. The hopelessness of a life in prison could be worse than the knowledge of imminent death. In that way, one can say that life in prison is a harsher punishment and therefore more satisfying than the death penalty.
One can argue that the death penalty is better because it is more just. It is unpleasant for the family of the murder victim to have to know that the killer is still alive. The murderer may be suffering, but they are still alive and most people feel that any life is better than being dead.