When comparing Sumo Paint vs PixiEditor, the Slant community recommends PixiEditor for most people. In the question“What are the best pixel art / sprite editors?” PixiEditor is ranked 17th while Sumo Paint is ranked 40th. The most important reason people chose PixiEditor is:
It's actively developed on GitHub under MIT license, and it's totally free.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Has most of standard Photoshop filters
Pro Has a Chrome App
Chrome app can be downloaded here.
Pro Has advanced layers support
Pro Can save to cloud, locally, or directly copy to clipboard
Pro Free and open-source
It's actively developed on GitHub under MIT license, and it's totally free.
Pro Very easy to use
Pro Stylus support
It has decent stylus support, erasing and drawing
Pro Active development
Pro Multi-document editing
Interface is dockable and supports editing multiple documents at the same time, even side-to-side.
Pro Clean and readable interface
UX is very similar to popular editing tools like photoshop, so getting started is easy.
Pro Multi-document edititng
Interface is dockable and supports editing multiple documents at the same time, even side-to-side.
Cons
Con Requires Flash
Con Slow to open
Sumo Paint is pretty slow to open when compared to other online photo editors.
Con Lacks drag and drop support
Doesn't yet support dragging & droping images in to the browser window.
Con Cannot zoom using mouse wheel
Con A little buggy
It's still in early development stage, so there are some bugs.