Much of the information about specifics when it comes to armor and weapons in WotR is cryptic, incomplete or simply unavailable.
There are a number of reasons for this. First of all, developers of the game have stated that were they to include all relevant information on how weapons work, each weapon would need several pages in the profile editor to convey all of the data.
In addition, it may be postulated that the developers have limited the ammount of information available in order to consciously prevent "number crunchers" from creating statisically optimized builds that would push the game's meta in the direction of masses of "clone builds" flooding the game. If this is the case, I would like to state my own personal endorsement of this policy.
Lastly, given the fluid state of the game's balance, much of the information that IS availabe through tooltips and graphs in the games profile customization screen is flawed or obsolete, and therefore of little help.

Given this state of affairs I hope readers of this guide will understand why I have avoided using specifics about relative comparisons between two or more items in a specific category. The purpose of the guide is to explain the underlying logic for why the game works the way it does.

P.S. I would like to thank jackx for bringing much of the information about the flaws in the games tooltips and graphs to my attention through his many cogent and informed posts on the forums of this hub.

Armor is divided into three categories:
1)Light
2) Medium
3) Heavy.
Each armor modifies a player's abilities in-game in three basic ways:
1) Damage Reduction
2) Body Coverage
3) Encumberance.
Generally the greater the damage reduction and/or coverage of the body granted by a set of armor, the more the player is encumbered by using it.

Damage reduction in WotR is calculated as a percentage. The percentage value by which an attack's damage is reduced is determined by the type of material the attack hits. Heavier armor materials grant a larger reduction. The types of armor materials are:
a) Cloth
b) Leather
c) Mail
d) Plate
Most armor types also have a small flat reduction which is factored in after the percentage modifier. It is important to note that most armors combine at least two of these materials. Which material ends up modifying an attack that hits you depends on what type of material that strike connects with.

Body Coverage

As stated above, armor material is not homogenous. A suit of plate will have areas that are covered only by mail, leather, or even cloth. The differences between sets of armor grouped in the same category mostly lie in how much of the body is covered by what type of material. Specifics are a little hazy, but generally, what you see is what you get. If one set of medium armor is all chainmail and cloth, and another combines mail with a breatplate over the chest, the one with the breastplate is going to protect your torso better.

Encumberance

Heavier armor materials increase encumberance more than lighter ones do. The more a player is encumbered, the slower they will be to accelerate when running, the slower they will be able to change directions, and the slower they will be at readying and swinging their weapons.

Weapons are both simpler and more complicated than armor. This is because weapon damage is determined by complex physics calculations which can radically alter the damage you end up doing against the same types of armor depending on; charge level, your movement/momentum, your enemies movement/momentum, and relative posistioning. These factors are a huge part of what determines success or failure in a fight and, in my opinion are the biggest selling point for the game.

Because of their complexity I won't be going into them for now, but it is vital to keep them in mind and use them when evaluating what is happening to you when playing the game. For now I am going to try and explain the various types of weapon damage and how they work.

Weapon Damage is divided into three types:
1) Slashing
2) Piercing
3) Blunt
These three types of damage interact differently with the various types of armor materials.

Slashing works great against cloth leather, and even mail, but is terrible against plate. Slashing damage also tends to have the highest base damage values. Weapons that focus on slashing damage also tend to have large striking surfaces and therefore large hitboxs, making them easier to land hits with. The best example being swords.
Piercing damage works pretty well against all armor types, including plate. Piercing also does a moderate ammount of damage. To deliver piercing damage you need to use thrust attacks, which can make you predictable and easy to block, or use weapons with "beaked" striking surfaces which have small hit boxes and are difficult to hit with. A good example of a weapon that relies on piercing damage is the chiaverina, but many weapons include the ability to do piercing damage such as both the prongeed and spiked billhooks or the one handed Battle Axe with its back-spike.
Blunt damage almost totally ignores armor, but also has the lowest base damage values. Weapons that utilize blunt damage also tend to be some of the hardest to hit with, as they usually combine smallish hitboxes at the end of some sort of wooden handle, requiring you to land your hits with the part of the weapon that is the hitbox, and not the handle. Good examples of weapons that deal blunt damage are the various one handed maces/clubs and the warhammer.

Many weapons combine more than one type of damage in the same way that armors usually combine more than one type of material. For instance swords can slash and thrust. Axes, while slashing weapons, will deal damage through plate armor much more than swords slashes will. The famed pollaxe combines all three types of weapon damage in one convinent package. A good melee profile will generally combine differnt types of weapon damage by using both primary and secondary weapons to cover all three bases. Alternate damage types can be accessed with many weapons by pressing the "Q" key to switch your grip.

When playing the game you can tell what type of armor is modifying the damage you are doing to your opponents by the color of the numbers the damage values are displayed in.

Red: This means your weapon's damage was unmodified by any armor at all and you landed a hit on your opponents bare flesh, well done!

Light Blue (Almost White): You have hit cloth armour, and your damage was hardly reduced at all, shame on you for picking on helpless peasants.

Orange: This means the damage hit leather armor and was only moderately reduced. It takes more than a nice jacket and a fancy hairdo to protect you in battle Mr. Fonzarelli.

Yellow: You have hit chainmail as can be found beneath the gambeson of the light armour sets, moderate damage reduction.

Blue: You have hit plate armor, high damage reduction. Best to switch to anti-armor techniques if you haven't already.

White: You have hit the opponents weapon or shield, stop fighting his equipment and start fighting him.

Any attack that hits and results in some sort of shield icon instead of damage values being displayed means the attack has been defelcted. Blue shields are armor defelctions, and white/gray shields are shield defelctions (i.e. you hit an opponents shield without damaging it).

A good combination of equipment is one that has armor which will provide decent protection without slowing you down too much (What counts as "too slow" is up to you), and a weapon selection that allows you to deal with as many types of armor material as possible.

There isn't usually one combination that will excel in all situations however, and what you eventually decide to use will have to involve tradeoffs. Everyone has their weaknesses and the key to mastering a particular combination of equipment is knowing whats its weaknesses are and compensating through your playstyle.

Keep in mind that both primary weapons, secondary weapons, and especially shields will have a big impact on your encumberance in addition to what type of armor you are using. Encumberance accumulates across armor choice and weapon choice, and can be partially negated by some perks.