Hi! Well, I've tried 3 stylos, that i used with iPhone 4 and Sketchbook Pro. So here are my rankings:

3rd place: The POGO stylus. It's nice and thin, but the tip is made of some sort of velcro, and after a while used to scratch my protective display-foils.

2nd place: A rather thick silver stylus, like a crayon. Tip is like a gel/silicone material. Brandname? Dunno. It has a softer tip than the POGO, but with the negative side of being really uncomfortable to hold after a while. And this statement is coming from someone with rather big hands.

1st place, no doubt:
The capacitive stylus from boxwave.com ... It's the perfect size (like a normal pencil or pen), and has by far the best responsive tip of all, which looks like a rubber-bubble and feels naturally when drawing.

Hope that helps anyone who's reading this.
Cheers,
Tom