Today I have tried a few digital drawing apps and explored the individual functions by trying to draw the same thing and compare. The apps I used are paper 53, sketches pro, forge, and concepts.
Paper 53 is a very famous app but I kind of feel it is for a certain level creative people. My fav feature is the colour mixer, it simulates the real colour creation process but with a digital advantage of change it back and force, and a material-waste-worry-free experience. This gives me a high expectation of real life drawing experience. However, the biggest drawback for me is the lack of pen tools (maybe I need to upgrade?) layers and size adjustment.
Forge to me is more like a product design app, where if you load an image and draw on a separate layer and then use it as a base to brainstorm many different variations. It has some strong marker pattern and size adjustment, however the pressure sense is not that great so you usually draw a very flat looking image. It would be great for graphic look. The old version used to have some template and gave you an inspiration of the type of result you can achieve.
Sketches pro is by far most natural to me. The learning curve is pretty low. It has many different pen tools which simulates the real life drawing the most compare to other apps( eg pressure sense and brush strokes). It has 3 layers so you can separate elements apart. Eg, give the outline a layer, colouring another layer and writing another. This is a dream feature for me when I draw on real paper. I was always concerned I would ruin my drawing with colouring. The only drawback for me is the colour creation. Unlike paper 53 you can create many accidental beautiful colours and add to your palate, sketches pro goes completely digital experience.
Concepts is a tricky one. It has so much potential than a simple drawing app but it has some steep learning curve before you fall in love with it. The wow factor for me are colour wheel: you can set up 4 tools with very specific details (tool type, colour, size,transparency) and self recognising layers. This layer feature sets itself apart from other apps because I found it is very easy to switch pen tool and forget to use it in another layer. The biggest advantage is the precision and this makes it superior to do architecture design and product design. The precision is reflected mainly in 4 ways. 1 it can show you the measure while you draw (eg how long the line is), 2 it can detect anything you draw, no matter whether it overlaps with other things or not. 3 the selection tool allows you to group or break up things easily, which makes it a perfect tool to come back and modify. 4 once you select partially or the whole image, it is basically a vector and you size it and flip it without losing any resolution.