Both KDE and Gnome are horribly bloated. I think Gnome is slightly faster though. Since you will probably want to get work done in class, you could look at more lightweight desktop environments. Xfce is one.
Well, there's a little bit more to it than that; KDE and Gnome are software suites. In addition to the graphical layer running on top of X (KDE was built on Qt, Gnome on GTK, IFRC), both are complete with text editors, file browsers, web browsers, chat clients, configuration programs, etc. I've been using KDE since I switched from Gnome a few years ago. Before then, Gnome's interface and software complement weren't as professional as KDE's (might not be as professional now, either, but I wouldn't know); my computer could handle the extra load KDE had over Gnome, so I switched and haven't gone back.
For slower systems I use XFCE, and for ancient computers I use Windowmaker and Enlightenment. XFCE comes with a few extra programs in addition to the interface, and Windowmaker and Enlightenment are pretty much exclusively interface.
I remember when Gnome was the bloated, sluggish one compared to KDE... but that was back when Gnome 1.0 was first released. Have you tried just using Windowmaker or something and then running a light desktop program on top of it instead? KDE and Gnome are convenient to use, but as Kris has noted are rather big and resource-intensive otherwise.