When comparing Google Tasks vs GTDNext, the Slant community recommends GTDNext for most people. In the question“What are the best cross-platform task apps?” GTDNext is ranked 13th while Google Tasks is ranked 69th. The most important reason people chose GTDNext is:
All the “Get Things Done” lists you would expect: next actions, someday, waiting, and scheduled.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Integration with Google Calendar
Google Tasks integrates with Google Calendar, consolidating your information in one place and allowing you to easily see which tasks have to be done on what day.
Pro Sync With Android
Pro Subtask lists
Each task can have a subtask allowing users to gradually break down a larger task into steps needed to accomplish it. When a user marks the parent task as complete, all subtasks inside that main task will also be marked as complete.
Pro Printable to-do list
Google Tasks allows users to print their to-do lists.

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 Inconsistent sorting when printing
You can start your tests online, but when you print it comes out differently.
Con Can print calendar or tasks but not both
If you want to see your day, you can see both your tasks and your meetings online. However, you cannot print it altogether as shown online. You have to print two separate things.
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
