But how can we measure the quality of the base system? I tried FreeBSD again a while back, but there were pretty bad bugs even in basic UNIX utilities like grep [1], some utilities + UTF-8, and I also had some kernel panics.

[1] I reported one of them in the FreeBSD bug tracker (+ patch). OpenBSD was actually really quick to solve this (I think tedu@ patched it), while the bug lingered for a long time with no activity on FreeBSD's end.