Not modes they are desktop enviornments. They have some small little differences.
If you are worying about installing them I suggest both. Since no one can choose better than you. Since these desktop enviornments are equally good and euqally populer. If U want one of them install KDE.
Links : Kde.org and
www.gnome.org
But you wont find much there.
But I must add that KDE is the default Desktop Enviornment on most distros. RedHat is the only onw I know that prefers Gnome.
By the way I like KDE while my brother preffers Gnome.
I some time wonder if richard stalman is the Gnome