Hello dear reader, I've been waiting for you to share my knowledge.
You've probably read several guides that took the same topic.
Most of them are very good and informative, so why should you read THIS guide?

Guides that have been made on this topic mostly tend to forget about several things You will learn here.
It's all connected with topic taken by one of my previous guides.
Topic about "benefits from piercing armor" [clickable link!].

Let's bring it on!

As you could learn from my guide about benefits from piercing armor,
Armor penetration works better when enemies have low armor.
Extra AD works better when YOU have low AD (because bonus is higher in percentage comparison).

So we can asume:
AD runes beat ARMOR PENETRATION runes when enemy has high armor, and You have low AD from items.

This is the very important point

From 3 quintessences you can gain either 7 extra AD or 10 armor penetration.

From 9 marks you can gain either 10 exta AD or 15 armor penetration.

As You can see, ratio of trade AD for AR.PEN. is better for quintessences than marks.
Calculations show that configuration "AD quints + AR.PEN. marks",
always wins over "AR.PEN. quints + AD marks".

This matrix shows difference of effective damage against target in certain conditions.

On horizontal axis You have target's armor, and on vertical axis You have Your AD (without runes).

Values in matrix' are differences between two runes sets.
To give better view I colored them with:
red color for AR.PEN. quints + AR. PEN. marks advantage.
blue color for AD quints + AR. PEN. marks advantage.

Stronger color means stronger advantage.



As You can see, AR.PEN. quints + AR. PEN. marks set wins only in case,
You have extremly high AD and Your target has very small amount of armor.
That situation is very rare, occurs only in lategame, and only against low-level enemies,
because skilled players always build defence.

Red color is again AR.PEN. quints + AR. PEN. marks advantage.
Green color is AD quints + AD marks advantage.

Stronger color means stronger advantage again.



As You can see, AD quints + AD marks set totally wins earlygame against any kind of enemies.
Difference is very high, regardless target's armor.

Only on moderate amount of damage (around 150+) set of AR.PEN quints and marks wins.
On top of that, advantage in that case is extremly high.



NOTE: Colorful fields of advantage are almost the same if you compare bare AD mark and AR.PEN. marks.
This may be helpful in case you use some utility quintessences and don't know which marks to take.

Colors stay the same. Green for AD quints and marks, Blue for AD quints AR.PEN. marks.



You can see that full AD runes set advantage is very small, and in extremly rare cases,
while AD quints AR.PEN. marks set easly gets advantage, and the advantage is very high.

The matrix above shows total values of effective damage of full AR.PEN. runes set.

Red color shows where that set is better over any other set.



The matrix above shows total value of effective damage of mixed AR.PEN./AD runes set.

Blue color shows where that set is better over any other set.




The matrix above shows total value of effective damage of full AD runes set.

Green color shows where that set is better over any other set.

It's very common mastery, I'd even say it's pretty much standard.
In previous matrixes its influence wasn't taken in consideration, my bad.
After comment I immediatelly prepared hotfix in my calculations and...

...nothing really changed.
Difference is not really amazing:

Mixed AD/AR.PEN. runes set stayed almost the same comparing to others.
This is because due to flat armor penetration it has,
the mastery doesn't work really well against low armor target,
but it still has extra AD to recompense it.

Full AD runes set's advantage slightly grown against full AR.PEN. set,
but it isn't very strong difference.
This is because percentage penetration doesn't work well against low armor targets.
And on high armor targets it already had rather high advantage over full AR.PEN. set.

Full AR.PEN. set's advantage slightly decreased over other sets.
This is because percentage penetration works less effective with already high flat penetration.

The difference is around 0-1 point on edges of advantage fields.
So colorful fields showing where is certain set better almost didn't move (5 cells on each matrix)

I decided not to post new matrixes as I want You, readers, to not get You confused during your read.

For general use, AD quints+AR.PEN. are best.
That set wins earlygame when You have low AD and enemies are squishy,
it wins midgame when values are average, and lategame, when Your AD and enemies' ARMOR are both high.

Full AD runes set is good only for champions,
that don't buy much AD and are meant to fight high armor targets.
But after all, difference isn't so high to justify that choice.

Full AR.PEN. runes set is good only in very lategame when You have extremly high AD,
and only when You fight targets with extremly low armor (as for the game time).



I'd recommend having AD. quints AR.PEN. runes set as it clearly wins.
Wins throught 90% of games and 90% of cases.
This is by far best runes set for physical damage dealers.
Finish him!
The only situation you may not want to use it, is when you want to use:

• Very specyfic character, like Akali
• Champion that is hybrid AD/AP, like Jax
• Other Quintessences in addition to AR.PEN. marks, like Greater Quintessence of Life Steal.
  Don't read tags!

That's all in this topic.
Hope now you have crystal-clear knowledge about runes sets, and I answered almost every question.

Although if You still have some problem - post it in comment. I'll try to help you.






Don't forget to vote.