When comparing Paint.NET vs MyPaint, the Slant community recommends Paint.NET for most people. In the question“What are the best free Photoshop alternatives?” Paint.NET is ranked 5th while MyPaint is ranked 11th. The most important reason people chose Paint.NET is:
Unlike most photo editing software, Paint.NET is simple to learn and easy to use. This means less time is spent learning the in's and out's of Paint.NET and more time on photo editing. For those who only edit photos sporadically and don't have time to invest in learning complicated tools for editing, Paint.Net will suit your needs.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Easy to learn and use
Unlike most photo editing software, Paint.NET is simple to learn and easy to use. This means less time is spent learning the in's and out's of Paint.NET and more time on photo editing. For those who only edit photos sporadically and don't have time to invest in learning complicated tools for editing, Paint.Net will suit your needs.
Pro Free software
There is no charge for this software; but donations are welcomed.

Pro Lightweight
Paint.net provides a streamlined but effective core tool set. Support for advanced and niche features is provided through modular plugins, allowing the user to install only what's needed.
Pro Actively developed
The project is active and being continually expanded and refined.
Pro Active and friendly community
The forums are filled with tutorials, as well as people who are friendly and eager to help.


Pro Plugins allow extra functionality
Plugins can be made by anyone in the community, and are offered for download on the forum. They extend the capabilities of Paint.NET to cover most tasks.
Pro HiDPI support
Paint.NET supports fully HiDPI displays, with no scaling problems.
Pro Interface gets out of the way
MyPaint mostly consists of the canvas. The interface to select different brushes can be brought up if needed, but it generally stays out of the way of getting things done.
Pro Good support for pressure sensitive graphics tablets
MyPaint was designed specifically with pressure sensitive graphics tablets in mind.
Pro Good media emulation
Pro Forgo the need to resize the canvas
If a user needs a bigger canvas all they need to do is zoom out instead of re-sizing.
Cons

Con Only available on Windows
Paint.NET is only available on Windows.
Con No project-based interface
You can only edit a single image at a time in Paint.NET. For example, in other tools you can open 5 or a 100 images at the same time, and stack those windows in all directions.
Furthermore, when you are editing in Paint.NET you can only "view" a single image at a time, even though you can have multiple images open. This limits your zooming ability, as the image will go fullscreen quite quickly, and hide parts of it behind the floating toolbars which can not be embedded anywhere on the screen.
Con Is not stable at all
I could not even open a png file to start without the software to freeze.
Con Not a lot in terms of image manipulation
MyPaint focuses only on drawing. It has very little in terms of post processing or image manipulation features.
