by Questioning_LifeSomeone I know who would make it fast and painless.
Sounds like you need a basket of kittens......
Anything that could keep you from being directly involved, getting someone else to do it for you. And having an alibi or what not.
But if I had to do it? By method of poison, normally it is not a suitable method of murder because the cause of death is strange so a toxicology test is done. However, there are poisons that can look like natural causes, but they will even show up in a toxicology test, I think it is hard to commit the "perfect" murder. In any situation that I can think of you are going to leave behind some form of evidence.
You have to remember, you could be the most clever and calculative murderer alive. But there is an equally clever detective, who has the resources and time to pursue you. Murder should be your last resort, it is reckless and very risky. And the consequences are very high. There are otherwise to accomplish the same result.