When comparing Asana vs GTDNext, the Slant community recommends Asana for most people. In the question“What are the best cross-platform task apps?” Asana is ranked 12th while GTDNext is ranked 13th. The most important reason people chose Asana is:
Asana has fantastic mechanisms for dealing with team collaboration. Not only can tasks be assigned to team members, but Asana lets users follow tasks and use hyperlinks to refer to team members within a task.
Specs
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Pros
Pro Powerful team collaboration features
Asana has fantastic mechanisms for dealing with team collaboration. Not only can tasks be assigned to team members, but Asana lets users follow tasks and use hyperlinks to refer to team members within a task.
Pro Free for up to 15 users
Pro Simple workflow
The Asana task workflow within a project is broken down into "Today," "Upcoming," and "Later." The tasks themselves have the status of either done or not done. There is also a subtask feature to group tasks together. Tasks can be assigned to other team members and are stored in the "Inbox" view for processing. This replaces email for some team communication.
Pro CSV export and print
Pro Very polished interface
Teams can have private (only visible to project members) and public (visible to anyone in the team) projects. Each member can also have their own personal projects.
Tasks can be viewed in list and calendar views. It's possible to display only the tasks assigned to the user or tasks organized by project or team. Single tasks can exist in multiple projects. Lists of tasks can be divided into sections and organized in many different ways – tasks that still have to be done, tasks that have been completed, by due date, by assignee, by popularity, etc.
Expanding a task will allow adding things like subtasks, tags, and attachments, as well as comments. Users can also subscribe to a task via RSS from this view. There's a separate view specifically for attachments.
Search lets you find what you’re looking for quickly.
Pro Tagging system allows easily filtering tasks
The tagging system enables project managers to easily filter tasks.
Pro Provides lots of help for getting started
There are many videos, tutorials, and reference documents to help you get up and running.
Pro Supports Kanban and list views
Asana provides a list view and a Kanban view which can be selected if a new project is created.
Pro Well thought out keyboard shortcuts
Keyboard shortcuts all involve the Tab key, so it is unlikely that they will interfere with shortcuts that have already been established.
Pro Integrates with Slack
It's possible to have tasks appear in a Slack channel.

Pro GTD style lists
All the “Get Things Done” lists you would expect: next actions, someday, waiting, and scheduled.

Pro Automatic next actions
When it comes to choosing your next action, most to-do apps suffer from the same problem: All of your actions (sometimes hundreds in total) are visible to choose from. This can overwhelm users and cause them to give up on the system. GTDNext is different. In the "Next Action" view, only the very next action is shown for each of your projects. This results in a nicely consolidated view of only the things that need your immediate attention.

Pro Unlimited levels of projects and actions
In GTDNext you can set up an unlimited number of levels for your projects and actions, allowing you to plan your project and sub-projects in as much detail as needed.

Pro Areas of Focus
GTDNext supports the “Areas of Focus” methodology from Getting Things Done. You can filter all of your tasks to just show your work tasks, side project tasks, or personal tasks. There is also a global filter, so that when you’re hard at work you can focus only on your work projects and tasks.
Pro Option to visualize all projects and tasks in a single outline view
This is really useful because it prevents you from having to navigate through each project individually.

Pro Many keyboard shortcuts available
The number of keyboard shortcuts makes it easy to log or add tasks without removing your hands from the keys.
Cons
Con Mobile version lacks calendar
Asana's calendar is present in the web version but is conspicuously missing in the mobile app.
Con Unable to manage multiple workspaces
Each "workspace" or "team" in Asana is strictly isolated. You cannot see your personal tasks versus work tasks or collaborations together, you need to log in to a different profile.
Con No task dependencies in free version
Dependencies is only available only to Teams and Organizations on Asana Premium.
Con Can not use list view and board view for a same project
Asana can only choose one, either a list view or a board view.
Con Strange UX with strange workflow
Similar to task the manager in Todoist or Wunderlist, but not too complex for under four members.
Con UX Design is overly opinionated
The workflow is not very customizable, which forces you to use a flow that may not be your preferred or best option.
Con No mobile app available
Con Web only
GTDNext does not have native apps for other devices, but it does work across PC/Mac/Linux on the web client.
Con No Google Tasks integration
