1. Quick - Gun
2. Access - Hanging
3. Painless - Inert gas
4. SI - If you plan CTB, you will always feel the Survival Instinct.
This is our nature.
But I will choose Inert Gas.
You lose consciousness quickly and it is effective (if you configure the set correctly).
This may allow you to calm down a bit before CTB.
Additionally, you can take some medications, etc.
For example, benzos.