The best Medium Armor - Elder Scrolls: Morrowind
In Morrowind Medium Armor is generally considered to be the worst armor skill in the game for one main reason. Medium Armor barely offers more protection than Light Armor (in some cases it does offer less protection) and it weighs substantially more. The rule of thumb most players follow is if you want to play a warrior class and wear good armor, just use Heavy Armor instead. Otherwise just stick with Light Armor.
The main area that Medium Armor excels when compared to Light Armor is through Enchanting. Most of the game's Medium Armor has higher Enchantment Values than Light Armor which means you'll be able to apply more powerful enchants on each piece of armor.
Best Armor Rating Per Slot
Helm: Adamantium Helm
Chest: Ebony Mail
Legs: Ice Greaves
Boots: Royal Guard Boots
Pauldrons: Royal Guard Pauldrons
Bracers: Royal Guard Bracers
Shield: Ice Shield
Important: The Armor Ratings you see in my screenshots below may be different for you. The amount of Armor Rating a piece of gear gives you in Morrowind decreases or increases depending on what your skill level is with that armor.
Ice Armor, also known as Stalhrim Armor is a set of Medium Armor that was added into the game during the Bloodmoon Expansion Pack. To get your hands on a set of this armor you'll have to complete about half of the East Empire Trading Company quest line - for more information check out my How to get Stalhrim/Ice Armor Guide.
Depending on who you side with during the East Empire Trading Company story line you'll either have to pay 1 piece of Stalhrim or 2 pieces for every armor piece that you make. Siding with Falco is the best option since each piece of armor only costs a single Stalhrim Ore. If you side with Carnius it'll cost you 2 Stalhrim per piece.
All in all Ice Armor is not really worth going out of your way to get since it has got lower Armor Rating than both Indoril and Royal Guard Armor and it requires 100x more effort and time than either of those sets. The Enchantment Values on Ice Armor are not that high either.
Royal Guard Armor
Royal Guard Armor is a set of Medium Armor that was added into the game during the Tribunal Expansion Pack. This armor is worn by every one of King Helseth's guards in the town of Mournhold. You can find King Helseth's guards in the same building that you teleported into from Ebonheart. After you speak with Asciene Rane in Ebonheart to be transported to Mournhold simply run upstairs and you'll find the guards in question.
If you're already in Mournhold then use the Divine Intervention spell and it will put you into the Royal Palace Courtyard; the whole Royal Palace area of Mournhold is the main location where you'll find the Royal Guards. You can also find the Royal Guards roaming around the Plaza Brindisi Dorom area. Make sure you use Frenzy Humanoid or Taunt on them to provoke them into attacking you first to avoid any criminal penalties.
Indoril Armor is the armor you see worn by Ordinators in towns controlled by the Tribunal Temple such as Vivec and Ghostgate. Chances are if you've been playing this game for more than a couple of hours you've already been to Vivec and met some Ordinators - technically you can kill any Ordinator guard and get a full set of this armor without much hassle.
For a less violent way to get a full set of Indoril Armor, you can search the corpse of Feril Salmyn outside of Kogoruhn. You're sent to find this corpse during the Hair Shirt of St. Aralor quest but you can technically come here at any point and get the armor if you want it. Most characters I use Medium Armor on I come to this location as early as possible for a full set of Indoril.
Warning: Wearing the Indoril Helm or Cuirass will make you a target of all Ordinators. They don't like people wearing the sacred armor who aren't a member of the order and will attack you on sight if they see you wearing it either the Helm or Cuirass.