If you're telling me "you need stamina", then tell me "only if youre dual weilding daggers" because otherwise there's no point in bringing up stamina, is there?
No what im saying is, the general play style of a stealth thief will benefit more from an increased stamina and armour than he would from clothes enchanted for similar effects. Even if you go ahead and enchant your clothes for armour and health, you still would get the same if not more benefit from enchanting light armour with health. As you still get your armor and health values, but ontop of that increased stamina, Which as a thief is far more useful than the other stats.
Put it this way, robes: Either increased magicka, or health/armour enchants. Well.. the magicka isnt going to help you.
Light armour: Armour, additional stamina regen, health enchants . Same as the robes accept you get additional stamina. Which will help you in cases of melee fights, which as a thief is going to happen more often.
Unless your going for a magic based thief, using illusion alot, the magicka bonus off of robes (which 95% of them have) is irrelevant. Ontop of that, if you enchant those robes with armor and health, your essentially getting the same thing you would get from light armor with a health enchant on it.
At the base of it all, its pretty much a case of either:
- Which do you like the appearance of more?
- What playstyle exactly are you going for, Magic stealth or Weapon stealth.
If your going for weapon stealth then the stamina increase will help your archery with its "pushback/knockback" attack, and then if you switch to melee weapons when up close it will help there.
If your going magic stealth then go for clothes. The less encumberance means better sprinting away to safety, magicka bonus and generally looking more "magicky".