htop is usually the most correct one for endusers to read because it simply shows a sum of the actually used physical ram for applications (listed as RES in the app list as well) and comparing both htop outputs the values do not differ too much between your two systems.
the gnome tool seems to simply sum up the total of ram, buffers and caches which in the end should be as high as possible on a linux machine for performance but will not actually tell you a lot about application memory usage