I don't like painting on iPhone with any painting apps. Feel awkward scrubbing my finger on its tiny screen. But then, I try this AutoDesk SketchBook (iTunes link) and it suits with my finger. Of course it takes time to get used to painting on iPhone with this app. But it's just.. well.. feel right. Here are some works from my iPhone.
More about iPhone AutoDesk SketchBook
Free AutoDesk SketchBook Mobile iTunes link
$2.99 AutoDesk SketchBook Mobile iTunes link