The subject of the two Ghostscripts came up last October, but we didn't
really discuss it:

https://lists.gnu.org/archive/html/guix-devel/2016-10/msg00598.html

The canonical Ghostscript is developed by Artifex Software Inc:

https://ghostscript.com/

We package GNU Ghostscript, which is a fork of Artifex's Ghostscript:

https://www.gnu.org/software/ghostscript/

Both programs are distributed under the AGPL, as far as I can tell. But
Artifex Ghostscript is actively developed, which I think is very
important for C software that is designed to handle untrusted input.

If you are curious where Ghostscript is used, try this:

$ guix graph --type=reverse-package ghostscript | dot -Tsvg > /tmp/graph.svg