.Xresources or popup menu. Memory footprint is moderate.On: Artix Linux
From low to high in kB
Although xterm has the lowest memory footprint, it has only so when using bitmap fonts. Those have some disadvantages as not really being scalable. When using xft fonts the memory usage of xterm rises considerably.
urxvt was one a lightweight alternative to xterm. Now it has a bigger footprint then the mother of all X11 terminal emulators.
mlterm was surprisingly the terminal emulator with the lowest footprint when using xft fonts. Additionally it offers configuration by using a command line tool for experienced users as well as a GUI. So this is the recommended terminal emulator.