Procreate is one of the best iOS App for Artists. Procreate has a lot of tools you need to create awesome illustrations. The UI is perfect and usability frendly. Available from the App Store for $5.99.
Linea Sketch is a balanced tool for note, ideas and thoughts you have and like to visualizing it. The focus here in this tool is more on what you create and not what you have as a tool
Paper by Wetransfer is perfect for sketching, typing, paint and draw. Very quick and userfrendly interface. Nature gestures are supportet.
(cover by Allison Bagg)
Sketchbook Pro is a allround talent. You can create sketches with a lots of tools and the performance is strong. Sketchbook is made for young and old sketch lovers . Available from the App Store for FREE. Membership for 4.99 $ / Month or 29.99 $ / Year