What are the pros and cons of flat vs. scaling runes?

Upcoming Changes

Seems like Riot has targeted flat runes as being a source of balance issues. Be on the lookout for more flat rune nerfs and scaling rune buffs because if they are significant enough (say, scaling outvalues flat at level 6 instead of 13) then the flat runes have far less value than the scaling.

Here's a peek at the upcoming changes.

General Advice

In short, go with flat runes if you will have a significantly stronger laning presence because of them. Although scaling runes outpace flat runes around level 13 (sometimes even earlier), the strong early game presence provided by flat runes can out-value the late game presence provided by scaling runes.

To answer your questions more directly:

1. Certain champions that have high stat scaling or activated abilities use flat runes to significantly empower them early game. Some examples:

   • Champions with near 1:1 ability power to damage ratios on their abilities (Sion, Amumu, etc.) can turn an early game 50 ability power directly into 50 damage, which is scary for early levels when you have from 400-600 health as a squishy champions. You will have to be weary of taking damage from them as this will badly hurt your early game.

   • Crit builds, mostly crit Gangplank, rely on flat critical strike chance or damage early game to win the lane through big critical strikes when harassing. Anyone who's had the unfortunate experience of being killed by a huge crit during a low-level duel knows how strong this can be, albeit very luck based.

   • EDIT: This has since been changed but I'm saying it for historical reasons: Akali's Twin Disciples passive used to provide 10% spell vamp and 10% bonus magic damage when she has a bonus of 10 attack damage and 20 ability power, respectively. Having this at level 1 or 2 is very appealing, and this is what pro Akali players tend to do, including the top Akali Westrice.

2. You should never buy less than Tier 3 runes. Tier 1 and 2 runes provide small bonuses and may be responsible for at most 3-5 of your low level wins, but once you hit level 20 you'll be glad you saved your hard earned IP for Tier 3 runes. Runes cannot be bought with RP so you'll be forced to grind for them, which I've been doing for the last 200 games and I'm still not finished. You will still win plenty of games without a rune page before level 20, speaking from personal experience.

3. There is always a certain level at which scaling runes outpace flat runes. That level is usually around 13, but as stated in this answer some outpace at level 6. Almost all of the time you need to measure the utility you get out of your runes by yourself, because their value is largely based on your skill and style. The exceptions I know are that flat Armor, flat Magic Resist, flat Attack Damage, and flat Ability Power Quintessences are are far more valuable than scaling because of how important those stats are early game. Early game farming and presence is very important, which you will learn with time and I won't cover here. Flat Mana Regen runes can also help early game sustain.

Referring to playstyle:

In terms of offense, flat runes are really worth it if you can use them to force enemy champions out of their lane and zone them early game. For example, if those flat runes get you three waves of creeps and 1 more kill than your opponent, you have a ~800 gold advantage that more than makes up for the stats lost by taking flat runes over scaling. This is most commonly done by killing your lane opponent and pushing the lane to their tower.

In terms of defense, I always use flat runes to counteract the power of others. If your opponent happens to use a strong combo of flat runes on a champion in most cases you will be crushed in lane (read my answer to #1). By starting with flat runes like Armor yellows and Magic Resist blues I get a great +13 Armor and +13 Magic Resist. Health Quintessences are also decent. They mean you can basically ignore enemy champion harassment for the first 5 levels and farm as you please. There is nothing more discouraging to your enemies when they can't force you out of lane after trying their hardest.

Dominion

I've racked up a lot of Dominion games and came out deciding that my advice on flat runes still applies to Dominion, if not more than in Classic gameplay.

This sounds odd given champion level increases so quickly in Dominion, meaning scaling runes reach their potential faster. However, scaling are only viable if you can farm properly and prevent your opponent from killing you. In Dominion, there's no consistent farming and you have to fight! If you're staying in lane farming you're likely going to fall behind everyone else who is focusing on getting kills and capturing points. So you can't reasonably expect to avoid fights and just farm. You're going to be fighting opponents with all-in flat rune strategies, and with scaling you're likely going to be losing.

In particular the initial fight for the Windmill happens at level 3. At this level flat runes still provide more power than scaling, so they are important to have if you want to win that fight. If you don't win that fight you tend to lose the whole game - all 4 of your teammates dying at the Windmill is a ~500-1400 gold advantage that the enemy team has (depending on how many of them died), and with that gold difference you can have a very hard time catching up.

There are basically two factors to consider:

1. The level at which flat + scaling pairs of runes 'match' - that is, provide the same benefit regardless of which type you have - varies a lot between runes. Ability power Marks, as you posted, match at about level 6 (.08 * 6 = .48). This makes scaling AP Marks relatively more attractive than, say, scaling Cooldown Reduction runes. Scaling CDR runes ("Celerity") don't match flat CDR ("Focus") until level 13.

2. Certain stats are more helpful in the early game or the late game, suggesting the use of flat or scaling runes respectively. For example, mana regen is very useful early and mid game, when you want to be able to stay in lane for a long time without having to go back to base. In late game, after a fight you're more likely to be going back to base anyway. Magic resist, on the other hand, is often considered more useful in the late game because it's helpful to be able to survive a burst of magic damage in a teamfight, which doesn't happen as much early game.

Usually scaling rune are more effective late game unlike flat rune which happen to be better early game.

Usually, I prefer scaling runes so that the power of my champion keeps progressing. But I mostly play carry AD or support champions. If you are to go jungling, or are in need of kills early in the game, you can favourite the flat rune to give you enough boost to perform your tasks.

Maybe flat runes can be more effective on 3v3 games, since they tend to be shorter games than 5v5.

My personal rule of thumb:

• If you're an aggressive player, go for flat runes.
• If you're a defensive player, go for scaling runes.

In theory, this applies to all ranks of runes. In practice, once you hit lvl 20, you'll never again care about Tier 1 or 2.

Reasoning

Aggressive players tend to initiate fights early in the game, often before minions even spawn. At lvl 1, the difference between a flat armor seal and a scaling armor seal is huge.

Deffensive players tend to hug towers more, and generally rely on later-game team fights. After lvl 8, most scaling runes will begin to surpass flat runes, making for a stronger late-game hero.

As for certain runes being more superior, they each give advantages at different parts in the game. It's more important to build them into an overall strategy with a specific champion than it is to always pick certain runes.

References:

• http://na.leagueoflegends.com/runes/3
• https://docs.google.com/spreadsheet/ccc?authkey=CKPPzIEP&key=0Apz-hn2_2cmbdHlQX0ZDMndwM041WHY5bUU3c1NDZkE&hl=en&authkey=CKPPzIEP#gid=0 (check crossover level to see when scaling runes equal flat runes)
  edit: this spreadsheet is no longer accurate