Jax is an excellent late-game melee duelist, dominating most melee champions with his versatile kit (E, Ultimate).
Maximize dueling power with E (Counter Strike) for damage mitigation and R (Grandmaster's Might). His primary weakness is sustain, so compensate with runes and items.
Strong against melee but weak versus ranged poke champions like Quinn or Kennen. Avoid first-picking to prevent unfavorable matchups.