I acquired one of each, and then tried them all on a variety of paper. The class of the field was the Rapidograph (fizzygeek greeted this finding with "Duur!" – she could have saved me a bunch of time). It pulled a nice neat line, of consistent width and solid coverage, over everything I tried it with. It also feels very nice in use, and didn't misbehave even if I held it at an angle, like a calligraphy pen, instead of vertical, like a drafting pen. Next in line was the Micron, which needed some care to produce a solid, even line on some surfaces. Then came the Sharpie ultra-fine point, which wavered more and didn't feel like a fine writing instrument. The Staedtler worked like a cheap felt-tip marker, and felt dry and uneven.
The feel and line quality wasn't the only thing I was evaluating, however. The Rapidograph doesn't work out of the box. You have to fill it with ink and get the ink flowing. It's quite a little ritual to get it ready for use. This doesn't bother me, as coffee, tea, and aficionados as well as most musicians will understand. A little ritual is nice to have, and helps get you in the mindset for a task. However, it doesn't lend itself to off-the cuff usage. The Micron, on the other hand, is ideal for spur-of-the-moment use. You take the cap off and start drawing. It's always ready, and doesn't need any special care. It's also inexpensive. The Sharpie was similar, ready for use any time you want it. The Staedtler has an interchangeable cartridge system, so you can use the same barrel with different cartridges for various line widths. It also advertises that you can leave it out, with the cap off, for up to eight hours without it drying out. However, the ones I got had already dried out with their caps on, so I'm a little dubious about that claim.
Satisfied that the Rapidograph would suit my needs, I decided to pick up a couple more widths, in the fancy jewel tips (better feel, longer lasting). However, the jewel tip pens are no longer made, so I hunted around some to find some old stock and replacement nibs, so I should be in jewels for a long time to come.