I used Sketchbook for a while (iPad), but it just never ‘clicked.’ Nothing was bad really, the brushes just never quite worked with what I was trying to do. I was really just sketching though, didn’t get far trying painting. Then I found Infinite Painter and that really works well. I just recently bought the full version as the value is definitely there for me (I particularly liked that they had a ‘Proko Brush’ which did a reasonable job replicating Stan’s soft lead with overhand grip, then sealed the deal finding the Wet Marker brush which is great to paint with). Haven’t tried Procreate, paying up front without trying it didn’t interest me and I prefer supporting a diversity of tools rather than just going with the most popular one blindly. I also use Krita, which has come a long way and is incredible as a free product. It’s a pity guides and demos on the net are almost universally Photoshop, thank goodness Marco Bucci’s recent course here also covers Krita :)

Yeah I use Autodesk Sketchbook, becuase as you said its free. But its also light weight and has PC, IOS and android versions too. I think its very popular amoung people beginning digital art, and you will find incredible artists on youtube who use Sketchbook. I think what is lacking with Sketchbook is lack of clipping mask layers, lack of liquify or warping tools, and the color balancing tools are very basic. However if you dont care about those things, it's a pretty nice option.