I started with Windows, played around with KDE3 a bit in my early days of Linux, settled on Xfce and GNOME 2 as my preferred environments and once GNOME 3 happened and KDE 4 stopped sucking as bad, I used it for a little while. I've also briefly used OpenBox, in the form of CrunchBang and LXDE.
Eventually, it became clear that I was going to be getting a laptop at some point, so I decided to learn about tiling window managers and try several of them out. Having to use a touchpad or drag out a mouse every time I wanted to get on my laptop didn't exactly sound exciting (or acceptable) to me. Out of a long list I tried out, some of the most memorable and my favorites included dwm, xmonad, spectrwm/scrotwm (boo to the developers for the name change... pussies!), notion, and i3. A few others a had some fun with were euclid-wm and herbstluftwm.
In the end, I have decided to settle on i3, and that is what I am using now. I love it--I have been using it since before I even got my laptop, and it's still my primary choice (even as a desktop window manager). Avoiding the mouse by using tiling window managers has improved my wrist... fewer aches and other odd feelings. Well worth the learning experience and effort to switch. As an added bonus, I get much, much better use of my screen, with next to no effort on my part, and absolutely no overlapping windows.