Following a recent clean install of Debian, I added LXDE and XFCE desktops to allow usage comparison. Switching between them after a couple of days allows assessment of usability, functionality, eye-candy, and response.
Both are light 'n' fast. There are a lot of features in Gnome and KDE that I don't need or I don't use. I don't need much from a desktop and don't use many bells 'n' whistles. I avoid clutter, and look for a fast, responsive desktop/window manager hybrid with minimal features.
I work mainly in Emacs, XTerm and Chrome (or Firefox/Iceweasel). If I could work without a mouse, I would. But I haven't been able to crack that one yet. Browsers are geared towards mouse selection. Keyboard selection is difficult, but that's a post for another day.
XFCE and LXDE have a number of useful features, such as:
1. Mouse wheel on desktop switches workspace
2. Drag browser off screen moves window to next workspace
3. Edge resistance adjustment
4. Window border snap adjustment
5. Focus to follow mouse
6. Mouse wheel on Title Bar rolls up window
XFCE by default opens all windows in center screen. It stacks XTerms on top like a deck of cards. To change this, open 'Window Manger Tweaks' from the main menu.
Click Mouse > Settings > Window Manager Tweaks > Placement
Adjust the slider marked 'Minimum size of windows to trigger smart placement:', to the left to reduce window size.
I guess the most impressive feature of both XFCE and LXDE is fast response.