As an ADC main I have delved lots of hours into completely learning the role. I didn't play ranked this season because of how bad the role got near to mid season but i believed it is now better. From playing lots of games as each ADC and having a very good understanding of the game I will be telling you who to ban as each ADC.

Ashe: Ashe is immobile and her highest counter is Miss Fortune, yet I believe that when playing Ashe a skilled player can win a matchup against Miss Fortune, yet assassins are far more countering to her. I suggest banning the most broken assassin at the current moment who is currently Kayn.
Caitlyn: Caitlyn isn't the most safe ADC to play, her only escape being flash or E so you need to ban a champion who can punish that in the mid-game. That champion is typically Ezreal, Jhin or Draven. I think Draven is the best ban.
Draven: Draven is a broken champion and has been for a long time. He doesn't have any particular counters yet his weakest point is short trades in the early game. Ezreal can exploit this with a good support so when playing Draven, Ezreal is a good ban.
Ezreal: Ezreal is a very safe ADC to play and is only countered by waveclear. As many people will know, Sivir has the best waveclear so she is the champion you should ban.
Jhin: Like Ashe, Jhin is countered by assassins yet also waveclear and aggressive supports. Leona, in my opinion, is the best overall ban for any Jhin player.
Jinx: Jinx is a great late game hypercarry who deals a sufficient amount of damage at all stages in the game. Her biggest counter is a support who can engage onto her who is also too tanky for her to kill at that stage. Alistar is an example of this and he is arguably the best support in the current meta; he is the best ban for a Jinx.
Kai'sa: Kai'sa is my current favourite ADC and I play her in a hybrid way lots of the time. I have very rarely lost when playing her and most of the time it was down to bad support play or my own mistakes in not playing around my team. Yet the people who kill me the most are top lane bruisers and Lucians. Banning Lucian is suggested by me and be careful of top lane Irelias and Garens.
Kalista: Kalista is a very good early game champion yet she falls off quite a lot late game compared to other ADCs. Banning Caitlyn is best because she can keep up with you early with her range and outscale you late game.
Lucian: The most notorious early game lane stomper is Lucian. His only counter I have found when playing against him is Sivir and engage supports. Sivir focuses on pushing waves and not taking bad trades. Sivir is a good ban if you can play against an engage support well.
Miss Fortune: Miss Fortune is not very mobile and her R requires her to be stationary. Her biggest counter is an ADC or assassin who can jump on top of her. Rengar or Kha'zix is the best ban, yet also Twitch or Kai'sa is a good option.
Sivir: Sivir is an ADC who specialises in waveclear, to counter her you need to play a champion who can trade into her and also scale into the game. Tristana can do this and is a good ban if you want to play Sivir.
Tristana: 'The Yordle Gunner' is an incredibly late game force with both her passive and scaling. When playing her Caitlyn is her biggest counter as she has large range to punish your short range in the early game.
Twitch: Twitch is the best late game carry according to most people, only being rivalled by Vayne and Kai'sa. Twitch is most punishable in the early game as he deals no damage, so Lucian or Ashe are the best champions to ban.
Varus: I haven't played much Varus yet I can see why he is a good ADC. He is very immobile yet has good synergy with most supports. Yet he can rely on abilities and Soraka's silence is very good at countering some of his main damage outputs. Soraka is a good ban for you and the entirety of your team.
Vayne: Vayne is a very goo late game threat and is fairly mobile. His biggest counter is Draven who can punish him in the mid and laning phase. Draven is also broken and should be on Riot's nerf list so ban Draven.
Xayah: Xayah and Rakan are quite unstoppable as a duo. Yet Alistar and Leona counter them so a ban to either of those, preferably Alistar, is best.

Thank you for reading. Some of these ADCs I have guides on and I am updating them as you most likely read this for the latest patch. As an ADC main I will be making as many ADC guides as possible. I hope to one day become FNC Rekkles, maybe you will be too. Check out my 'Who shall I main' series on my blog if you want to. Thank you again and I hope this helped you.