When comparing GTasks vs ToDoList, the Slant community recommends ToDoList for most people. In the question“What are the best offline to-do list apps for Windows?” ToDoList is ranked 4th while GTasks is ranked 15th. The most important reason people chose ToDoList is:
Cost, percent done, priority, you name it - you have it. If you prefer simple layout - no problem. You can configure everything
Specs
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Pros

Pro Unlimited subtasks
Unlimited subtasks or sub sub tasks, as deep as you need, excellent for project work.

Pro Closing parent task closes sub tasks

Pro Synchronizes with Google tasks available natively in GMail
Seamlessly syncs tasks.

Pro Available on iOS

Pro Works with Chrome's 'Google Tasks Panel' extension
Pro Great functionality, lots of options
Cost, percent done, priority, you name it - you have it. If you prefer simple layout - no problem. You can configure everything
Pro Comments with richtext format
It means comments can have different fonts, links to the pages or links to another tasks. You can format text your way.
Pro Multi-level subtasks
Pro Configurable calendar view, day view, Gantt chart, Kanban
Pro You can set as many filters as many columns you have, as well as export your view or single tasks
Cons
Con No recurring tasks fom completion
Con Pop up ads get in the way
The app frequently displays popup ads when you navigate the app, forcing you to pause to close them.
Con Does not support attachments
You cannot add attachments to tasks.
Con Android app is in early stages still
Only the Windows version is fully-featured. The Android app is still in early development.