Brush and pencil options
Brushes are a fundamental part of digital painting.
Brushes are probably Krita’s strongest area. For a start, there are masses of them, divided into categories and each with its own colourful, custom icon. The downside is there’s a bit of ‘settling in’ time while you learn to navigate around them all. If you did need a type of brush that Krita doesn’t come with, then you can probably create it. For instance, you could take an existing brush and edit it so that it, say, darkens and blurs according to pressure setting or stroke speed, and that interface is nicely done.
All of GIMP’s brushes are fully configurable, and just clicking the Brush tool makes this apparent, because the left panel (by default) is filled with many options such as size, angle and hardness. If there was a brush type that you couldn’t find, it might be possible to approximate it by changing the parameters or loading in a custom brush shape.
The brush facilities in MyPaint are extensive. By default, the selection isn’t as extensive (or overwhelming) as Krita, but if you right-click one, you can open the brush editor which has dozens upon dozens of subtle options. The tool options dock, with parameters such as brush size and smoothing amount, is neat and simple. As always seems to be the case with MyPaint, these areas look simple at first, but have a surprising amount of depth.
Inkscape has good facilities for brush-based art and customisation of brushes, but like most of that program’s features, it takes a bit of work to figure out how to do things.