Ahri or Jayce

I honestly think Ahri is better. She is safer pick and is still strong even when behind. Jayce has to be fed or just be useless.

Better, nicer, more CC, more mobility , hentai, health regen, best midlaner now that Viktor and Azir are nerfed and she's fun to play

But why not both ? :)

Get Jayce, then you can play both top and mid

Jayce can go anywhere, so there's that. Get countered in a lane? Go to another.