Hanging works for me. In the town square, by the county sheriff.
Lots of problems with firing squad and/or hanging. Most have to do with lawyers. Firing squad requires dealing with the cleanup and possibly contaminated (HIV) blood. Hanging gets into ripping heads off of fat people and not enough drop for slight people ... etc.
With the Nitrogen Asphyxiation, they go to sleep. Nothing for a lawyer to try and hang his hat on. No cruel and unusual, no blood, no “excessive” pain, always works, no drugs to expire, run out of , or manufacture to withdraw.