I'd never used scaled before so with this character I decided to. Since I got the perk to make it, I made a set for my character and then a set of Steel Plate for Lydia.

It turns out that Scaled armor (at least the cuirass) provides better protection than steel plate. So seeing that, I made a set of scaled for Lydia, and gave it to her and she promptly equipped it. But the thing is, scaled is a light armor and Lydia is supposed to specialize in heavy.

Does the follower equip the highest rated armor regardless of it being light or heavy?

Also, it's peculiar that despite its inferior protection, steel plate is worth almost twice what scaled is. And it's even more the stranger when considering that female NPCs look way better in a full set of scaled than a full set of steel plate.

That's how I understand it and has been my very limited experience.

Bingo. Their own specialization doesn't matter; they'll take whatever armor (or weapon, for that matter) offers the highest stats.

I know this is right and I think it's even based on the base stats. Friggin' Mjoll equips the damn Ebony Great Axes every time I hand her one to carry out of Nord crypts even though the Legendary Ebony Greatsword I made/improved for her does more damage.

She should have gotten a job as the Executioner.

Now this is interesting. I don't have the Glass Smithing perk yet so I can't make/improve a glass weapon that's as good as any steel weapon I improve. Right now Lydia has a Legendary Steel axe that does 24 damage and glass sword that does 20. She always equips the glass sword. And that's not the first time I've noticed it. I've seen this happen with other weapons as well. It seems as though they don't recognize an improved weapon over an unimproved one. The only thing they seem to recognize is that glass is potentially better than steel. ebony better than Orcish, etc.

At least that's my experience on this particular matter.

She likes the Dwarven Great Axe that my other character gave her. I don't use her as a follower on that character, but she walks around Riften with it on her back.

FWIW Mjoll cuts enemies down waayyy faster with the Improved Greatsword than with the normal Great Axe, but, yeah, they seem to base their decisions on base damage.

If only tavern clothing had a high armor value...

No, Scaled Armor has a BASE AR of 32, Steel Plate has a BASE AR of 40. The values you see are actually influenced by your current skill in Heavy/Light Armor.

If you have Light Armor at 60 and Heavy Armor at 15, of course Scaled is going to show up as giving you better DR, because you're proficient in Light Armor.

Lydia is wearing Steel Armor as her default outfit, not Steel Plate armor. Steel Armor has a base AR of 31, that's why she's picking Scaled over Steel (because they choose armor depending on the base AR).
But she will still have better DR with even the base Steel armor because she has a higher skill in Heavy.

I'm not so sure about that. Erik the Slayer has higher skill in light than heavy armor. He starts out with Iron Armor, but gladly equipped Hide Armor (which has lower base value if I understand correctly) when I gave it to him.

Not true. I tried countless time to have Sven use a steel warhammer, or a steel battleaxe, both a lot better than his ancient nord greatsword. He never agreed to it.

I've actually seen some inconsistency with this. Lately, Lydia has been sticking two handed weapons in her inventory in favor of a sword and shield, and occasionally a bow and arrows.

They use bows and arrows when you use melee weapons, even if they don't have one in their inventory.

Ah yes. Now that makes sense. I was grinding out dozens of sets of Legendary Steel Plate armor last night and in order to lighten the load on the way to sell them I gave her as many as she could carry and she immediately equipped them even though she was already wearing Legendary Scaled.

But it doesn't seem that wearing scaled makes her significantly weaker, especially considering that I Wabbajack her every 5 levels or so.

At any rate, my Smithing is now at 100 and I have the Dragon Armor perk so as soon as is possible we'll both be wearing Dragonscale. I'm sure she'll be just fine with it. She's certainly not going to be wearing Dragonplate, that stuff is Fuggly.

And then there's this. She's supposed to be proficient in 1H but give her a battlaxe with higher base damage and she'll immediately equip it. But she always has a bow.

You can actually make followers wear clothes if they are your spouse and/or if you have the Perfect Touch perk (and their default gear will never reset). http://www.youtube.com/watch?v=SdtFtjMikqA works for spouses/followers and http://www.youtube.com/watch?v=zSBNYOyWfgQ works for essential followers.

If you have the UFO mod the housecarls are reset to two handed over one handed.