xmonad dual-head for ~1.5 years now. i use a near-vanilla config; all i've done is thickened the window borders and changed their colors. i also added alt+down to launch pcmanfm (i use the mouse for that and i have a tenkeyless keyboard so it's convenient) and alt+o to launch ranger (which uses the vi keys).

it's tiny, fast, and very reliable. the way that windows appear and organize themselves makes complete intuitive sense to me. there's a master and secondary area. the master area contains only one window by default, but you can increase/decrease that with alt-, and alt-.; new windows open on top of the currently focused window. there are 3 default layouts -- master on the left, master on the top, and monocle (all fullscreen). i experimented a lot with layouts in dwm but i eventually realized what i really wanted was the default xmonad behavior.

the desktop system (you've got 9 virtual desktops by default, selected via alt-1 through alt-9) lets me easily swap the contents of one monitor to another, even though they're different resolutions; all the proportions and relationships stay the same. it's "greedy" swapping, so if you're on one monitor and select a desktop that's currently visible on the other, they switch displays. on the rare occasion that i need to float a window, it's quick and easy (alt+click to drag and/or alt+right-click to resize, alt+t to push the window back into tiling) and behaves just the way i need (always-on-top, focus follows mouse). everything except moving and resizing floating windows is a keyboard shortcut. all other window managers seem cumbersome to me these days.