I think for the same reason that lethal injection isn’t always reliable: doing it well and painlessly requires physician assistance, and physicians refuse to assist in executions.
In most US states (and this is a matter of law, unlike the above), physicians are not even allowed to assist in suicides, even if the patient is terminally ill and living with incurable pain. That means physicians don’t even get much if any practical knowledge of euthanizing humans.
Efficiency? Well, you don’t have to pay an electrical bill for a hanging, so unless the rope breaks hanging is certainly more efficient.
Also, if you hang someone by the neck long enough, or electrocute someone long enough, they will die 100% of the time. So I guess that would be a tie, unless of course the rope breaks and you need to replace it and hanging them on a second rope counts as 2 hangings.
Messy clean-up afterwards, unless a flock of vultures is handy … :eek:
A bullet’s only 50 cents. 
Enzyme based drain cleaners
Well, they can’t clean drains worth a damn.
Oh, is this the wrong thread?
Where you buying your bullets?
I want to take hangmans’ wood into the next life.
Amazing! I’ve never met anyone before who had been executed enough times to have a preference.
I’ve never eaten a shit sandwich…but I know in advance I wouldn’t like it.
I recall years ago – early 1990s, I think – there was a hanging in Washington state. Can they choose between two forms of execution there? I think the perp chose hanging to make a statement about the barbarity of the death penalty, intending for the witnesses to be shocked. However, the witnesses reportedly said it seemed quick and efficient, over in a flash.
What would Rasputin have chosen?
“All of the above”, of course.