Interesting. The first four responses are four different methods. Which shows that there is not any one way that is best for everyone. What you need is the method that is best for you.
To me, the best way is the way you can. You need to be sure. If you flinch or close your eyes at the wrong time you can injure the bird instead of cleanly killing it or you can injure yourself. You need the right equipment and you need to be able to use that equipment. There are little tricks that can make it easier.
I use the hatchet and stump method. I have a stump (actually a tree trunk section cut off that acts like a stump), I still have the strength, coordination, and eyesight I need, and I grew up using axes, hammers, hatchets and such so I am confident in my ability to hit the target. I don't recommend this method for everybody.
I have no idea which method will be best for you. Some version of the kill cone seems to be most popular with newcomers, but even there you can slice the jugular so they bleed to death or use something to cut off the head.
My suggestion is to ask for details on a specific method and ask questions. See if it is something you could do.