Procreate recent upgrade (ver 1.7 ) made it an extraordinarily powerful app. It is one of the top art app for iPad. Since its painting engine is complete based on openGL, it can take full advantage of the GPU instead of clogging the CPU. Key features are - a polished interface, the possibility to create your own brushes and a freely rotatable canvas. Procreate also has a fantastic user guide book which is downloadable to iBooks.
ArtRage features some of the best paint simulation on the iPad. It attempts to simulate real-world traditional oil, acrylic and even water color paintings on iPad. Blending of colors is really awesome in Artrage as it understand canvas texture, wet paint and can sense paint quantity on the canvas. Artrage is also available for Desktop user with more advance features and at a higher price. It is a must have app for iPad Artists!
SketchBook Pro by Autodesk is one of the most popular iPad art apps with digital artists. There's a wide range of digital pencils, pens, markers, and airbrushes to choose from, all accessed via a simple but intuitive UI that lets you pin toolbars to the screen for easy access. One of the great plus is the ability to import and export Photoshop-friendly files. It also has a free version of the app called Sketchbook Express.
Paper captures your ideas as sketches, diagrams, illustrations, notes or drawings and share them across the web. It has some amazing watercolor effects. The app has some limitations including not able to zoom and inability to change brush sizes, still it is pretty powerful and neat painting app.
Doink is a simple but powerful animation app that lets you create your own library of drawings and animations, combining and remixing them in an endless variety of ways. Great for beginners and pros alike. We have mastered this app and combine art and animation using this app.
There are many more apps in the App store and one is free to pick their own. We focus on the technique of art creation not just the app.