Just wondering.

I outfit my Lydia with the best that can be had as I'm counting on her keeping some baddies busy. Most of the ones I've had will only outfit HEAVY armor so I give them a full set of enchanted Dieretic. Enchantments I equip them with are: Warmth. Firewalk, Grounding (Ring, Helmet, Boots), Armor of Stanima Regen and Gauntlets for two handed. Their long sword has a lifesvcking enchantment.

She'll still knell from time to time but by then we've cut through most of the baddies. She and I single handedly killed off ALL the guards in Markarth one day while in the middle of a quest. After realizing what we'd done I reverted to a Save game to before we got them all after us.

The Gauntlets for boosting 2-handed does NOT work on followers.
Here are the enchantments that DO work on follower apparel:
Copied from UESP:

• Fortify Health
  
• Fortify Heavy Armor
  
• Fortify Light Armor
  
• Fortify Magicka
  
• Fortify Stamina
  
• Fortify Unarmed
  
• Muffle
  
• Resist Fire
  
• Resist Frost
  
• Resist Magic
  
• Resist Shock
  
• Soultrap/Fiery Soultrap
  
• Waterbreathing (Followers can't drown anyway, but this stops them surfacing for air)

Thus, you are better off changing the gauntlets to something that actually does anything for followers.
(Fortify caryweight doesn't work on followers either.)

I give Derkeethus glass armour and weapons.

Housecarls get Steel Plate, the Companions Wolf, Dwarven, Ancient Nord and Glass atm. I've almost completed my 1st set of Ebony but haven't decided who will get that. Vriddi refuses to wear anything other than Orcish herself.

I usually give em a enchanted sword, and thats it. Well, and maybe a shield. Its not like i need to take care of them anyway, since only i can kill them.

Current running Illia in much better gear than my own character has - She's in Daedric armor and Ebony boots / gauntlets, I'm in Orc Armor + Gauntlets + Ebony Boots. We both wear ancient nord hemlts, best looking in game and nice face view. Mines the "of the Unburned" model (only way to get Fire Resist on head that I know, and its better than I can enchant), her's boosts Destruction spellcasting. Didn't know followers were limited in what they can benefit from - guess I'll be re-doing those destruction enchanted items. Shame, I liked the look of her Ancient Nord Helmet, not sure I have another handy.
Illia has a bunch of staffs, including dual fireball staffs (which works well with my 90% fire resist) and also has a unique shield (+resist magic, + helath) from a quest and a legendary ebony sword with drain health 30 (more loot).
My followers typically get the "best" gear I find / can make, while I use stuff that's optimized to my skill set, which pretty much just means the best greatsword I can make (no enchant needed) and whatever heavy armor is "good enough" for me to max out rating (pretty easy in heavy armor for me, and I can mix and match freely) and has better resists than I can enchant, or I put bonus health / 2 handed damage on.

I've given Derkeethus some good light armor, a greatly improved ebony bow, and a number of improved swords with good enchantments.

He still uses whatever he finds off the ground. I checked his inventory today after a week of putting it off and found he'd picked up four hunting bows, two imperial bows, two falmer bows, two long bows and one enchanted bow. He went through a phase earlier where he picked up pickaxes; now it's bows. : /

I still like the guy. And I still indulge him in exploring those caves he seems to love so much.