I feel that I'm using both ways.
I use the GTD system to keep track of all the things I want to do—to remind me that I want to do those things and give me a rough time line of what to do when. Often seeing the list is enough to inspire me to want to start working on something.
Yet - I prefer not to make myself do anything that I just don't want to do unless the consequences for not doing it are severe. Most of the things on my list I do happily (internal motivation!), and if I change the deadline on a particular task too many times, I see it as a sign that I didn't want to do that thing as much as I thought. At that point, I re-examine why I thought I wanted to do it and either rediscover the original motivation or delete the task from my list.
Fortunately, I have set my life up in a way so that I have a LOT of control over what I do, and other than paying bills, doing taxes, etc, there's very little that I didn't choose to do. Once I make a commitment to someone else, I keep that commitment, so I aim to be very conscious about what I schedule with other people.