You need a minimal base OS to have the flexibility to build your own stuff on top of it, and you don't want to be at the behest of another corporation. That rules out Fedora, Suse, and Ubuntu. You also need it to be popular and have good hardware support. So the only two realistic options are Arch and Debian.

My guess is that Arch is easier to build on top of because they have a stronger culture of leaving packages as unmodified as possible relative to their upstream sources, whereas Debian maintainers seem to have the opposite culture. A Debian system has a lot of Debian-isms in it overall, whereas the Arch-isms tend to be more like generic sensible defaults rather than OS idosyncrasies.