My favourite design software is Paint Tool Sai.
I’ve been using it for 6 years as a digital art program and I definitely see it as more of an artistry tool rather than a professional design tool - which is what I see Photoshop as. You can create your own brushes easily by either editing the properties of an existing brush or creating from scratch. I personally grab pre-made brushes from the Sai community online and edit the properties of the brush while I work. There are two types of layers, a normal layer, and a line-work layer. You can create lines and smooth editable curves in the line-work layer. The lines you make in this layer also have editable weights, pressure, and colour.
One of the functions Paint Tool Sai has over Photoshop is the Stabilizer tool. There are two levels in this tool, 1-15 or S-1 to S-7. Some artists choose not to use this tool at all while some rely heavily on it. When drawing usually lines come out with a slightly jagged look to them due to the natural movement of the hand. The stabilizer tool gives lines a smooth look, with the smoothness increasing with each level. Levels 1-15 give smooth lines without lagging the brush behind the mouse. It is my understanding that the ‘S’ in the S levels stands for slow, as in these levels the brush moves slower than the mouse for easier control. Personally I use level 0 for everything except for hard-edged line-work. I use S-7 for bold line-work such as stickers or logos. For other line-work, I choose somewhere in the low S levels.
To me, Paint Tool Sai is perfect for non-professional design work. It doesn’t have any typography tools and lacks the gradient tool. It is great for digital painting and illustration - and I much prefer sketching in Paint Tool Sai than in Photoshop.
With Sai I have created: sketches, lined work, paintings, character reference sheets, stickers, posters, and logos. Any sort of sketching and rough planning I would definitely choose Paint Tool Sai due to the tools provided and how familiar I am with it.