Originally Posted by TheOneMillion
It all depends on what mage. Mpen does more damage than AP on spells that have high bases but semi low scaling, and even then, it matters on the enemys MR, if you have voidstaff or not, and how much AP you already have. AP Quints will do more damage than Mpen quints o most mages early game when your spells have low bases and your champ has almost 0 AP, and will slowly drop to a little less damage than Mpen quints as you start to pick up more and more AP. If the enemy starts getting high MR though, AP will usually win out against FLAT Mpen. Of course, when they start grabbing ANY MR, you should grab Voidstaff (Easily the biggest damage increase for the widest range of variables).
Well, see this is why I believe in Magic Pen because now it is not useless after grabbing a Void Staff.
Most of my champs have a lot of high base damage, Ahri, Lux, are my main mids. I have many others, but those are my main two.
I just feel that 8.5 Mpen Vs 14 Mpen, or if I get the oppurtunity to face AD I get 20 Mpen, Which is 44 or 50 Magic Pen, which means with the 8% Mastery they would have to have around 60 MR to even start nullifying any damage.
I rarely get past my third item on my APCs because the game is usually over, and unless I'm getting MR stacked, I never get a void staff before my third item.
I know a lot of it has to do with preference, but I find myself doing more damage as early as level three. Usually because on Both Lux and Ahri I level my damaging spell twice to get that extra harras instead of getting my utility spell.
I base my AP Carries around those two because they are the ones I take into ranked, and they are the ones I win with.