I have always enjoyed sketches and line art. Do not get me wrong, a colorful pieces are great. Though, there is just something about rough sketches and line art that I have always enjoyed as well.
I have printed out a couple of the line art drawings for people to color in. It is fun to see how someone takes your art and builds upon it. If more of the people I know request some line art to be printed so they can color it in, I might consider doing even more of this. For now, I am at least keeping copies of the line art of pieces I am working on otherwise in case people are interested in some coloring pages.
Most of the time, I use an iPad Pro with an Apple Pencil and the application Procreate to create digital artwork. I like this combination because it is like having a digital sketchpad that you can carry around with you fairly easily at all times. It is easy to use wherever you like, at a table, on a couch, while lying in bed, outside sitting in the shade, and so on.