User blog comment:Shinaliss/Efficiency Plots of AD and AP vs Penetration/@comment-5686533-20140908051733/@comment-6000413-20140908104650

As I state in the blog, I consider LW above 200 armor, VS above 65 MR and I condiser you ALREADY have VS above 200 MR and go back to flat penetration, thus leading to that steep decrease at 200 MR.

The armor plot, on the other hand, is strongly biased by the extreme cost-efficiency of the brutalizer, but you also have to consider that tanky champions easily get over 200 armor. This means that you should buy a brutalizer early in the game, when armors are below 100. After that get AD if you have a very good scaling or upgrade the brutalizer (and maybe get another one?) if the scalings are mediocre (Talking to you Heca). Over 200 armor a LW would be useful.

You should buy ad only if you want with other important stats (crit, sifesteal, as, penetration itself)