I use Autodesk's SketchbookPro with stylus on Galaxy Note 3 to do portraits.

The pressure sensitive stylus and the ability to select pencil sizes and darkness makes it as real as sketching it on paper. Now I can sketch on the go..

 Click on the thumbnails for more details..

Digital Portraits - My teachers from Sainik Schook Balachadi

Digital Portraits - Family

Digital Portraits - People and Places