I haven't tested blag neither dragora but I have opinions concerning
Trisquel, gnewsense and Parabola:
Parabola is ideal for a person who needs the latest packages avaliable, and
they are mostly vanilla. Being on the edge have its drawbacks like the fact
that the system is more prone to brake in comparison to Gnewsense and
Trisquel, but I can say that Parabola is surprisingly stable.
Trisquel is somewhere between gnewsense and Parabola in terms of stability
and packages avaliable. One of the main advantages Trisquel have over the
others is the fact that there are a lot of customize packages made by the
team behind the project like the compton package, the custom Gnome desktop
with notify-osd enabled, orca, ubiquity, plymouth, Abrowser, icecat and a lot
more. Not only that but it is more secure than Ubuntu, have better defaults
and, oh goodness, it even have better design than the distro it comes from.
Well, I couldn't hide my enthusiasm and I compared with Ubuntu because I feel
it's more than just a copy with some packages removed.
Gnewsense si very close to Debian, sadly, it almost does not have diferences
with the distro it comes from not counting the fact it have scripts that make
esier the maintenance easier. Stability is it's main advantage.