What kind of marks should I use as jax?

armor pen.
it'll increase your burst, and plus, your AS is increasing exponentially anyways. a measly 20% from runes isnt going to help much, whereas full apen marks could mean up to 30% extra damage.

Disagree. Jax deals 50% magic and 50% physical damage with his skills and every 3rd hit from his ultimate dealing 300 magic damage, not to mention leap+empower harass. Buying either form of penetration is not particularly efficient on him. Front-end attack speed gets your stacks on quicker, exponential like kwj said above me, so you might get 10 stacks of your ult and 8 stacks of rageblade in 7 seconds instead of 12 seconds if you got some front end attack speed. Also allows you to jungle much smoother at level 1 if you choose to jungle jax.

AS marks

Getting arp or mpen won't make big diffrence

Armor Pen. Dont get AS

AD marks, AD or AP quint, ap/lvl blue
You scale off of power, not penetration, gogo get imbahp rapelane

So no dodge quints?

Why would you take 10 physical damage per hit from armor pen when you could increase the rate at which your guinsoo's and ult stack as well as the frequency of your ult's magic damage?

With just AS marks you get like 15-20% attack speed. With armor pen marks you get like 9.x armor pen. So what do you want... A free longsword or a free dagger? I'd take the dagger personally since it synergizes with his ult so well.

Arp helps early game mostly farming as there isn't much standing around banging it out with people early. AS really only starts making a difference at level 6. Mpen only helps early game harrass and really isn't noticeable if they get merctreads on top of base MR.

AD=vent damage as a longsword 9.2 or something. longsword dmg = 10 damage

AS=vent speed as a dagger 14%. dagger = 15% speed. Synergizes with Ult and Hybrid build extremely well. Only becomes really noticeable after level 6.

Arp has been proven time and again to be more effective early damage wise then damage marks. Better for early game farming and the rare stand there and bang it out scenario.

Mpen better for early game harrass and possibly farming. Pretty much reduced by 25% usefullness come mid game when most people will have merc treads.