Last week, I wrote that i was still looking for a window manager that I really like. I have tried all the mayor tiling ones and I finally settled with Xmonad. Yes, the window manager with the 300Mb haskell compiler dependecies. I’m okay with it now.
The way xmonad handles two (or more) screens is the way all window managers should do it. You have one set of workspaces. The screens are portals to these tags. So you can have workspace one on screen one and workspace two on screen two. Then you can have workspace two on screen one and workspace four on screen two. A picture to demonstrate:

The configuration file is easy to edit and I like it a lot. Even more so then the config file of awesome. It sounds scary to edit a haskell file but haskell is a nice, easy to understand language. My config file is found here.
So the reason I sticked with it were the multiple screen support, config file and the simplicity. I know a 300mb dependecy for a ~1 mb window manager is not really KISS but the way XMonad works is really KISS. That is because only manages your windows. You can choose youre own panel(if any). I like it!