I am an Xmonad user that tried Awesome, and the main thing that didn't work for me is that it seemed that Awesome workspaces (tags) were tied to particular monitors. Perhaps I just didn't take the time to figure out how to do it properly, but that was a deal-breaker for me.

In Xmonad, I have configured twenty different workspaces, and I can easily swap them in and out of any given monitor. With a triple-monitor configuration, this is quite handy.