Who should I choose ?

Hi guys, Originally, I play jungle when playing with a premade, or mid/top once solo. But after playing my placement games, I noticed a crucial point : at lower elos, the adcs feed a lot. I thought I can take advantage of this to rank up, since I am good at this role too (for the info, I am a polyvalent player). I already play Lucian and Vayne, but the first is picked a lot and the second have a lot of counter picks. So I thought I will buy Jhin or Kalista, but I still hesitate. Who should I buy ? Thanks for answering ^^