In my opinion the best currently is ratpoison, but it's a little hardcore if you're not used to it and might be scary to the average Joe. For him then IceWM is by far the best for this usage, I think. Low weight, fast, not as fast as ratpoison, but stylus-clickable. I've experimented with many. In my view anything heavier than IceWM is unusuable on the Uni, too slow...
That's also why gdm is too heavy and you have to use xdm.