I haven't tried LXDE all too much, but I've had many problems with the settings manager in Xfce, but I really like the custom dpi setting in Xfce, decreasing the dpi to force a smaller and neater desktop makes it perfect for small low res screens.. In general I feel that Gnome/LXDE/Xfce has way to large fonts and everything.. maybe there is a similar setting in LXDE too, but if not, I'd recommend Xfce..
And while I know you are thinking of LXDE or Xfce, I've had pleasant experiences with Gnome and KDE as well, although somewhat slow, I feel Gnome has the nicest launcher that reacts to the win buttom (I didn't manage to bind it to win in KDE because it insisted that it is a modifier key..) and even if the launcher is slow, if you write out what you want to launch and press enter, it will launch it regardless if the launchers animation hasn't fully loaded, in KDE you need to wait.
On the other hand KDE in general acts as I want it to for multitasking.
While these two felt just a bit slow, this is on a 32bit 1.6GHz dual core Intel Atom with Ion, 4gb ddr2 and 128Gb crucial m4.. so with a decent laptop it will probably be no problem.
There is no default launcher in Xfce/LXDE/E17 that works as I want.