Encoding gurus, I wish to learn!

[Losko]

Hi everyone, I've been reading at these pages for a long time and now I want to post my question.
I often manage with DVD authoring (in a way, I have fun with it, but my eye aiming to quality) so I am aware of video and audio encoding issues. I really appreciate Hank work (I use HCenc as my favourite encoder since version 0.22!) but also I look with great expectations at x262 developing.
Now, after reading these pages, a question raises about encoding quality.
Aside from the encoder you can choose, the quantization matrix (QM) has a relevant role in order to get more quality with the same filesize (or the same quality in a smaller file).
[I have surfed the web a lot, I'm quite familiar with math and matrixes, so now I think I now that a QM is]
I'm aware there are lots of QMes out there, but the encoding pros providing them often don't write a single line to explain why their QM is good or why it performs better than others.
So, which one you have to choose? How am I supposed to choose among them?
Have I to encode my movie several times with different QMes in order to evaluate their quality?
And when I will choose the QM which offers the best quality at my eyes, will I use that QM forever?
And, aside from my simple eyes, are there objective tools able to show the quality (via graphs or others...)?
In short, is choosing the QM a trial and error procedure? Or is it a slow refinement?
(in other words, when I get a final encoding from a QM, does this result just say if that QM is good/no_good? Else, will I be able to choose a better QM starting from that encoding?)
Thank you all.