If you are looking to learn window managers... remember there are two primary styles:
1. stacking (the more popular)
2. tiling (more on edge due to its less common interface style).
The most popular stacking wm is probably OpenBox (OB). iceWM & fluxbox are close behind. My unofficial ratings.
The most popular tiler is i3wm (and variants).
Most people would recommend you start with some combination of those, I think. Before starting, you might want to investigate the types of wms and see which sounds like a good fit for you and what you want to do. Remember this is linux. You can choose; you can change. But I recommend whatever you do, learn & have fun.