What is the ultimate productivity system?

I recently started using Things 3 (https://culturedcode.com/things/) to "consistently clear my head" and it's been incredible so far. It really does feel like my decision making has improved and that I'm connecting dots/ideas I wasn't able to before.

Has anyone else implemented the GTD philosophy (with Things 3 or another tool) and has it resonated with them?

I included the key section from David Allen below:

In order to change—in other words, to progress—you need to clear your head. This kind of mind sweep is incredibly powerful. How do you do it? You externalize, you write things down as soon as they come into your head.

Cognitive scientists have made it clear that your head is a crappy office. It recognizes things in the present and makes momentary decisions quite well—better than a computer, in fact. But if you try to juggle more than four things in your head at one time, your decision-making power is denigrated.

By creating lists of thoughts and ideas, you take the first step in “cleaning house.” But creating lists is not the only step. You also need to examine what you write, interpret it, and take action. That’s the GTD path in a nutshell.

The truth is, this is a huge adult behavioral change. A lot of people are letting their thoughts run their decisions. Their minds have been unmanaged for years.

- https://www.earlytorise.com/getting-things-done-with-productivity-guru-david-allen/