From Ellis Hamburger at The Verge:

"If you're purchasing a stylus so you can write notes on your iPad, you're going to be disappointed. None of the styli I tested had narrow enough tips to provide the agility to scrawl anything but quick notes, doodles, and scribbles. But, if you're interested in drawing with apps like Paper, you can't go wrong with a few of these options. The Wacom Bamboo Stylus, with its combination of sleek looks, small tip, and great responsiveness is our winner for everyday use. If you're serious about writing on your iPad, the Adonit Jot Pro is the clear choice, while you'll have to be pretty careful with it. If you break the plastic disc on your Adonit, you'll have to wait for a replacement. The Kuel H10 is a fantastic and tiny won't-mind-if-you-lose-it stylus, while the Cosmonaut is unbeatable for diagramming or writing flash cards."

I've tried several of the ones tested.  Of those, the Bamboo works best.  However, one "boutique" brand (yes, I just said "boutique") that wasn't tested that I'm a huge fan of is iFaraday.  I started using their "Basic" model over a year ago, and just recently picked up the Rx II.  While these don't have the weighty feel that that Bamboo does, the writing tip itself is much better.  Very smooth.  Very clean.  (Here's a review of the "Basic" model.)