Brush I use for everything: sketching, inking, coloring.
This is the brush I use from everything (sketching, inking, and coloring).

Sketching & lineart: 25px
Fine Lineart & details : 10px
Coloring: 80px & 50px (for details & erasing)
Note: I use CSP default blur brush or gaussian blur to blur the hard edges when coloring.