To answer this question from Todd (who tweets as togotooner), I drew as fast as I could with different nibs.
The Platinum music nib was the easiest to draw quickly with. It was also the one that had the least line variation. The 1.5 mm Pilot Parallel pen was easier to draw with than the 2.4 mm. I found myself fiddling with the Sailor Fude, so that took more time. The edges of the cursive italic nib would sometimes catch on the paper, so I had to be more careful. The Waterman flex nib produced the most line variation. While not speedy, it wasn’t as painstakingly slow as I thought it would be.
For flat nibs (the spectrum of stub to music to crisp italic), rounded edges and generous ink flow aid nimbleness and a looser, more expressive drawing line. In general, the sharper the nib, the more difficult it is to draw with. With practice, though, the hand should get used to the “drag,” and compensate accordingly.
The tools you have dictate the solution. If you don’t have a bucket for water, you use your hands. If you have a pencil, you shade with the pencil on its side. If you have a 0.05 Pigma Micron, you crosshatch to make shadows. If you have a fine flexible nib, you bear down hard for a thick line where the shadow goes. If you have a Pilot Parallel Pen, you rotate the nib so its entire surface touches the paper.
I prefer fine flexible nibs for drawing quickly. Next in line would be Pilot Parallel Pens. Each kind of nib has its own lovely result, so learning how to use them can improve anyone’s library of drawing styles.
(Adding another comparison shot for Khaled.)