I was on a similar quest recently, ansand after trying different Ubuntu variants, Puppy and DSL, my personal choice is PCLinuxOS.
The base distributive uses KDE, but it has variants with Enlightenment, LXDE, XFCE, and Gnome. KDE, Gnome and Enlightenment would be too "heavy" for your laptop, but both LXDE and XFCE will work great. I think PCLinuxOS has better organized configuration and management tools then Ubuntu, clearer ways to configure everything, more stuff works right "out of the box".