Jax, if you're good at farming you can just outscale him.
Olaf vs Jax is pretty even in terms of 1v1 late game; In terms of actual autoattacks Olaf is better however Jax's counterstrike does give him an advantage.
I.E Passive: TIE Olaf AS buff will pretty much go toe to toe with Jax's AS buff; Olaf's attack speed will gradually increase to a maximum of 99 percent similar to Jax's attack speed increasing gradually to 72 percent.
Undertow/Leap strike: Undertow In a 1v1 undertow will provide far more dps; due to the refresh. It can also be used to kite jax slightly during the Jax's counter strike
Jax's W/Reckless swing : Tie Considering both Olaf and Jax will have 200+ resists late game Reckless swing will give very similar dps to empowered strike.
Jax's Ult + Counter strike/ Ragnarok+ Lifesteal damage steroid Jax's ult wil give higher reisists than ragnarok so Jax's ult is better in that regard. It will also provide him with good dmg every third hit. However this damage is outclassed by Olaf's dmg from his dmg buff (percentage hp ad buff is better than ap dmg buff since it will scale of crit/lifesteal and penetration as well as plainly providing more dmg). Now it looks very grim for Jax however his counter strike does give him 2 seconds of free hits (not 3 since the stun wont work). Now it all depends on how well Jax can use this counter strike cause other wise Jax will definitely lose badly. I think this will go Olaf's way because Olaf will slow Jax when he turns on his counter strike and walk away. This might provide Jax with 2-3 free hits as he will autoattack once when counter strike is activated he will then leap on Olaf and attack again to counteract the slow. But then Olaf will simply outtrade Jax at that point since he will have better sustain better, and better damage.
23/11/12 Me: WTF Why do you have 6 boots? NoobElise: Aren't I a spider?