I use the iPad app Procreate by Savage Interactive. It's the BEST drawing app in the App Store. Savage Interactive is four guys in Tasmania and they are working very hard to make the best app even better.
I don't work for them, but in all my years (too many to count) of developing and using software, these are the most responsive crew I've ever come across. Their software is elegant, the UI is clean and intuitive, the feature set compares well to some desktop apps, it integrates with Dropbox so sharing custom brushes is a breeze.
And it's only $4.99!
Please take a moment to visit their site and drop into the forums to see what others are saying.
Almost forgot. They have added support for some of the new pressure sensitive styluses.
I'll attach one of my drawings done in Procreate. My style is black an white. I have no trouble with the precise placement of fine details. If you visit the website, you'll see some of the amazing work others have done with this app.