one messy sketch brush - soft for sketch, med/hard for line.

One brush that is capable of multiple sizes.
Press soft for the big and soft, semi-transparent stroke.
Press normal / medium for fine line stroke.
Press hard for thick line stroke.
Adjust settings so that it feels most comfortable to you.
Brush tip is a custom brush tip made using a program called Rakurri brush tip generator.
feel free to experiment with the brush settings!