Krita is completely free and open source. They have raised a couple of successful Kickstarters in the past to get the initial financing and now they are accepting donations.

Krita's preset brushes are one of the default dockers. Each brush has a preview on mouseover that shows a detailed view of the type of brush involved. All the brushes also have useful and descriptive names such as "HP Pencil" or "Textured Fuzzy".

All the most used and useful tools are easy to find in Krita's UI and are often just one click away. They are not hidden behind menus or dropdowns.

Krita is getting constant releases with updates and bug fixes. New features are added at a pace that far surpasses the other alternatives.

Although the UI is rather busy, Krita is very customizable. The editing window can be themed and the sidebar can be customized extensively throw many dockers or panes.

Tiled view that shows your image tiled in the editor, and permits you to edit it as you are seeing it tiled. If the brush passes out of your texture, it will just automatically wrap back the painting to the other side of the original texture, while permitting you to paint and see the results on any of the tiled "clones". (the shortcut key to activate this is w by default)