Important to note the difference between an automated task killer and a process viewer which let's you kill tasks(manual task killer).
The manual ones are sometimes needed to kill rogue programs that will run forever once you launch them or that are otherwise hung up. The automated task killers are defeating the purpose of having a smooth-running system. They run in the background to kill idle tasks which weren't using CPU. The thing to do is not install apps that launch on startup in the first place if you can help it. This includes: no automated task killers, no anitivirus, no widgets, etc. if you can help it.