I discovered Nozbe first, and I realized again what I was missing using Backpack for Getting Things Done Backpack just isn't made for building a task database that connects actions with contexts and projects. An application built for that special purpose is naturally more comfortable and easy to use. And Nozbe is such an application.
But Nozbe also has its shortcomings. The Quick review on the GTD blog lists them, and for Julie Sohn's criticism, see my initial article I especially hate that every action has to be connected to a project. I'm just not that project-driven. While in the meantime, Nozbe got a new feature for adding custom contexts, it's still second place when I compare it with Vitalist.
Vitalist is a Web 2.0 application for the Getting Things Done concept, too. I like the interface because it's mostly text and uses pastel colours. Take a look at this screenshot of the input form for an action, and you will see that there is everything you need to get things done the Allen way.
The whole interface feels much more straightforward than Nozbe's. If I realize that I haven't yet created the corresponding project while entering a new action, I can just switch the project choice list to a project input field and add the new project name right with the action. But I'm not forced to choose a project if the action is a single one.
Vitalist covers all aspects of the GTD concept. There are not only next actions, contexts and projects, but also a sometimes/maybe list, a reference section and a searchable archive. Another important feature is that actions can have a due date and Vitalist reminds me in advance by email.
What impresses me further is the quick development of Vitalist. Since I started using it, three cool new features were added: you can now view contexts as tags, projects can have sub projects and a new add/edit form makes entering actions even easier now.
Vitalist is feature-rich without bloat, it's fast and easy, it's flexible and matures quickly. That's why I'll manage my tasks from now on with Vitalist.