Lorenzo, for me, I have no preference, although I love the look of well-made bullion (metal thread).
Some countries use bullion for their dress ranks, eg. France and Morocco, Singapore, to name a few, and they also use Lurex or some other thin metallic thread for their other forms of dress.
Some countries use only bullion thread or gold braid, eg. Thailand.
For me, it depends on what the "official" material is, they all have beauty in my eyes.
Alf