As you may know, RaspArch is an Arch Linux Live CD for Raspberry Pi 2, developed by Arne Exton, the developer of RaspEX and RaspAnd. The latest version available is RaspArch build 151107, which uses LXDE, Mozilla, Gimp and Kernel 4.1.12 as default.
Arne Exton has chosen to use LXDE because it is a very lightweight desktop environment and does not require too muck disk space.
But this does not mean that you have to stick with LXDE, another desktop environment being available via the default repositories.
RaspArch is can be downloaded for free, via sourceforge.