I use SAI! For this picture I pretty much only used this brush:
http://puu.sh/eLcRF/d7c4fa2234.png (Also my stablizer is on 5)

Please ignore the name of the brush(es), I had a field day renaming brushes in a stream once......lmao
But the base is the pen tool, the first default brush in listed any SAI. I usually use sizes between 30 and 50 when inking pictures like this (usually the brush size is a lot bigger than the lines I produce because I like having leeway to choose bold lines as I go without changing brush size, so this is a pretty pressure-sensitive brush). I primarily go pretty lighthanded on most pictures, but with quick brisk strokes to get those hard, thin to medium-sized lines. I use the pressure pretty sparingly unless I feel like going super bold. I'm also frequently cleaning and shaping up with a hard-edged eraser tool