Conqueror has been the rune that most Jinx's are currently running. While in the end it's up to preference, Conqueror right now gives Jinx and her kit extra damage and a bit of healing with domination second. Jinx's Q stacks conqueror so you can stack it up pretty consistently.

Is lethal tempo better than conqueror?

Lethal Tempo: Gain 110% attack speed after 1.5 seconds of damaging an enemy. this would increase our ADC's attack speed to 1.31 attacks per second. this lasts for 6 seconds and takes 6 seconds to cool down, the entire cycle takes 13.5 seconds. Conqueror: each stack raises the user's ad by 3, to a max of 30.

What should I build on Jinx?