About KDE 3.5: stuck after suspend/resume on my Z. My xfce config is broken after using KDE. It looks nice on the other hand, maybe I'll have to flash and start from a clean system again.
e17 : fun, fast, nice. Needs some tweaking and development to become the one.
matchbox : it comes with the rom, so it will probably never be anybody's favourite. We want to tweak and change our Z's, don't we.
xfce: my favourite, as most people already knew. What I don't like is the "panel always on top" (it wasn't this way in 4.0.6, where it could behave as a normal window). Some people use autohide, but I don't feel comfortable with it while using a stylus. I mapped full-screen-mode to alt-f, this is even better because it hides borders and window-title-bars as well.
windowmanager : never tried, I will soon.
icewm : should come with more eyecandy out of the box. I've seen great things with this one, but haven't got the patience to figure out how to set it up the way I've seen it.
fvwm : great support on pdaX, reminds me of my hp-9000 days (HP-UX) in the early 90ties. I kinda love it.
fluxbox/blackbox : haven't really tried.
About speed : besides starting time they all respond more or less the same (except KDE, which is a bit heavy). I don't shut down, restart my wm very often, so ...
About memory : I use 64/128Mb swap, never had memory troubles.
The good thing : choice !!!!
Don't look at numbers, pick the one you like !
Have fun
Chero.