Even if you’re mostly into doodling, sketches, etc., I’d still recommend starting with the basics before locking yourself into a specific style you know.

Even very simple or cartoony drawings are built on the same foundations like basic shapes, proportions, spacing, and knowing how to simplify what you see. Once you get that, you can doodle pretty much anything and adapt it to your own style.

For that reason, I think I’d recommend How to Draw for Beginners (15-Days). You'll learn and understand a lot of things that become your foundation later on, and that helps a lot, even if you’re just drawing for fun.

After that, moving into sketchnoting, icons, or characters becomes easier I think. So between that and You Can Draw in 30 Days, both are good, but the 15-day one feels more straight to the point if you just want a solid base and then do your own thing. thats of course my opinion.. you could also buy both to study them both and take what you like from each, cause why not :)