When comparing Paint.NET vs Photopea, the Slant community recommends Photopea for most people. In the question“What is the best photo editing software?” Photopea is ranked 7th while Paint.NET is ranked 12th. The most important reason people chose Photopea is:
Photopea allows dragging & dropping images in to the browser window to upload them and add to the scene.
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 Drag and drop support
Photopea allows dragging & dropping images in to the browser window to upload them and add to the scene.
Pro Very reactive on feedbacks
Pro Fast to load
Pro Can save as PSD
This means you can open these files in Photoshop, so if you don't have Photoshop on one device, you can still export your Photopea project and continue editing on Photoshop on another device
Pro Photoshop Like Interface
It has a Photoshop-like interface with most of its features for basic editing.
Pro Has many features
Pro Uses Photoshop standard shortcuts
Pro Requires no browser plugin
As it is an HTML5 application, running it requires no additional plugins on modern browsers.
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 Hard to get used to it at first
However, you'll get used to it later!
Con Has only basic filters and operations
