Hi,
I have several window managers installed but since last year my every day wm is windowmaker. It's simple, has interesting and a plenty of features, fast build and it cost me few resources (CPU and RAM) which is important when recording multi-track audio with dozens of efx plugins, per example.
Another cool thing about why I like windowmaker:
1. you can tell a dock to load an app, like opera, keeping the window hidden, so slow apps do not bother me on startup when I'm using another one while I wait.
2. you can tell an app to bind itself to a workspace. I use the main Ardour window in workspace "4" and the mixer in workspace "5". It's very useful.