I guess it's just personal preferance, but I'm almost always in a Helmet, Mask, or at least Hood. For Armor, it just makes sense, you get a 25 point bonus for each armor peice you wear, so it lowers the Armor Cap, and all of the useful Perks in those trees require you to wear one. I find that Wind Walker, and Unhindered alone are worth more to me than seeing my hairdo.
I agree on the Shrouded Hood, especially on the rest of the set, because of the gap in the neck, it looks crappy. However, the Ancient Shrouded Cowl matches up to the Nightingale Armor's high collar. While you don't get the additional Armor bonus from it, Unless I'm playing a Nightblade (Who Armor is a moot point for) the extra Bow damage is a lot more useful than the Illusion bonus ever is. I pretty much have to build a character to barely cast Invisibility with it to make that even desirable over a more useful enchantment. OTOH, the Shrouded Hood is probably the best looking one in the game.
For all my Assassin characters, I generally Mix&Match those two sets for the best combination of Looks, and Enchantments. IDK about Armor,, because that's an issue for Open Batle, which you avoid all together by killing from behind. Therefore, I even wear Master Robes of Illusion on the Nightblade set, because the Magicka Regeneration is more valuable than the Resistances on the Armor. That, and I think it looks cool:
BOT (For a minute there, I thought this was the Favorite Armor thread) That's Nightmer, who's name should be Obvious. His real name is Mesmiro, after a historical pseudo-scientist, who coined the term "Animal Magnetism."