When comparing Emacs Org-mode vs Google Tasks, the Slant community recommends Emacs Org-mode for most people. In the question“What are the best cross-platform task apps?” Emacs Org-mode is ranked 3rd while Google Tasks is ranked 69th. The most important reason people chose Emacs Org-mode is:
This app's flexibility is based on its minimalist approach, giving the user near-infinite freedom.
Specs
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Pros

Pro Ultimate flexibility
This app's flexibility is based on its minimalist approach, giving the user near-infinite freedom.
Pro Absolutely free
Emacs with Org-mode is free as in beer and free as in speech – that is, it costs nothing and it’s totally open source.

Pro Files are usable anywhere at anytime
Users are not tied to one service provider, program, platform, or database engine.

Pro Incredibly extensible
There are many plug-ins for Org-mode, including Org-habits and Org-notify. If Org-mode lacks some piece of functionality, it is very easy to add it.
Pro Agenda views
Pro Excellent unofficial Android app (orgzly)

Pro Offline support
Pro Efficient features for deadline organization
Pro Supports plaintext spreadsheets
Pro There are a lot of extensions, for exporting to html, bootstrap, js-reveal and much more
Pro Quickly add rich text
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.
Cons
Con Unintuitive user interface
The key combinations are unintuitive and difficult to remember. This is probably because there are a lot of hidden "modes" depending on where the cursor is. Actions aren't paired with reversing actions like in other todo apps. For example, hitting shift-tab does NOT reverse the effect of hitting tab.


Con Android app isn't very good
There are several user-created apps for Android, but none seem to offer the same level of functionality as other to-do apps.
Con Not really cross platform
Although it is possible to get a lot of it working, no all in one, sync included, out of the box solution is available for mobile devices.
Con By default, a hard-to-read display
The default way of writing an outline or checklist creates a very messy wall of text that's difficult to read with no vertical spacing. You can manually add vertical spacing, but the Org operations don't preserve it. There are pretty-display modes, but you need to remember how to enable them, etc. etc.
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.
