I'm playing with the Paper app by 53, and I'm using the Pencil stylus. I'll admit that it is pretty fun, but it lacks a lot of things that I would think very important in a digital sketching app. You can't color pick, and there are no layers. You also cannot import pic or photos.
The Pencil stylus is buggy for me at the moment. Sometimes I will be painting, and all of the sudden it will smudge or it will erase.
Anyway I did this sketch of a bus. I named it struggle bus because, well struggling.
I will keep trying this app out, but I may return it before the 30 days and save for a stylus that offers pressure sensitivity. We will see...