Which is best for a Mage Alteration protection or light armor?

Early levels i would go with light armor.. but when you get that special perk go with alteration and clothes ONLY

i wear robes with some light armor gauntlets and boots and robes but if you have a melee/tank companion they will take the attention and you just hit them with ranged spells

Mage Armor 3 is rather worthless. You will still get superior protection by using light armor in conjunction with the skin spells. They all become irrelevant later anyway once you get the Dragonhide spell, because it caps you out on physical reduction by itself.

It really depends on what you are willing to put up with. It kind of goes like this:

1. Alteration spell > Light Armor (at first)
2. Alteration spell + Light Armor > Mage Armor 2/3
3. Alteration spell + Light Armor <> Mage Armor 3/3 (depending on the armor you picked up and your perks)
4. Dragonhide > any of those, negating perks from both trees. It requires Master level Alteration though.

Dragonhide uses both hands, uses a ton of mana, has a 5 second cast time, can't move while casting it, and only lasts 45 seconds with stability perked.

It's about the role you want to play.

If you look at the numbers closely, fully perking into alteration gives you about the same armor as fully perking into light armor. It's about a 2% DR difference from dragonscale to ebonyflesh. Alteration has other advantages though, and completely improved mage armor is only.... 7 perks or so. Light armor costs considerably more. You also get the master protection spell which is pretty good in a pinch!

If you really want to make light armor better, you have to spend perks on blacksmithing.

But, if you're a battlemage type, heavy armor passes up mage armor pretty quickly. Even if you don't have blacksmithing perks.

People will qq all day 'mage armor svcks don't bother with it!' but look hard at the numbers. Fewer perks, only ~2% DR less than light unless blacksmithing is perked too, and alteration brings a lot of other benefits with it. Paralysis, anyone?

If you're spending on alteration anyway there's very little reason not to give it a go in mage armor. Unless you plan on doing a lot of melee.

1. Heavy > Alteration > Light
2. Heavy + Alteration > Alteration + Light > Mage Armor 2/3
3. Heavy + Alteration > Alteration + Light <> Mage armor 3/3

This of course counting the fact that you aren't using smithing. If you are using smithing both Light or Heavy on their own completely blow alteration out of the water with the exception of dragonhide but that requires a long cast time and frequent reapplication whereas straight heavy/light give you 80% reduction all the time without ever having to cast a spell. Only reason to wear robes is RP imo.

Yeah, it goes pretty fast. With just 3 perks and level 30 at alteration, you already get 120 armour (stoneflesh). And alteration also becomes useful for other things like paralyze.