There is not one.
Not a pro by any means but here is my opinion.
Kalista - Has the potential to snowball. Has a very high skillcap. (Though terribles will tell you otherwise) Requires support synergy. Technically does not have the most damage late game compared to other ADCs... Since her damage is completely reliant on activating her E. Where most other ADCs deal their damage immediately.
MF - Kind of fell off since they finally nerfed her back in line. She is an ultimate that is it. She can win lane, but she is an ultimate.
Caitlyn - In my opinion probably the best ADC for 80% of players. Her trap changes and silent buffs have made her huge. Her trap change especially is amazing. It gives her huge zone and damage potential. She still has the longest range in the game I believe. She does not depend on anyone else. She can win lane through her range and trap zoning, and her late game damage is one of the best.
Jinx - (Jinx What?) Probably the 2nd best ADC hyper carry in the game. Pretty big in Korea right now. Basically people are going IE - > Static shiv - > Hurricane. For 3x Missiles spam. The damage is stupid. Of course she requires time to really come online. She can lane safely if you are not terrible because of her rocket range. She is less popular in NA right now probably because she is not a burst champion. She always deals a ton of damage, but she isn't like Lucien who does a ton of damage up front, then drops until his abilities come back up. If you play safe and farm her damage is insane.
Kog'Maw - Probably the highest damage ADC in the game even after the changes. His laning phase has been nerfed which is the main point here. His late game is potentially better than Jinx, but he no longer has lane domination like he did in 6.4-5.
Ezreal - you see a lot of people in silver and bronze play Ezreal who somehow think they are good. They all go blue Ezreal. Well what you have to remember is Blue Ezreal is a poke and kite champion. His damage compared to other ADCs is much lower. When you look at stats after games and look at champion damage dealt, you have to remember that is game wide, which includes his poke. If we could see damage done by teamfight, he would be low. People play him because they think the outplay and kiting is cool. His damage is really low. Which is why you don't see him on the pro level at all. Or at least not in 6.5-6.5 that I can remember.
Vayne - I like to say Vayne is like the sun. The ADC at the center and all the other ADCs circle around her for their chance in the spotlight while Vayne remains unchanged. Always at the heart. Vayne's popularity is dependent on the meta. When the meta is heavy tank, suddenly people remember vayne. When the Meta isn't people stop playing her. She has not been nerfed, her damage is still insane. She comes online with only 2 items. I highly enjoy vayne because she is only of only 2? ADCs in which there is actual outplay potential. Everyone else is more point and click with a move here or there. Her tumble and condem gives her the best outplay potential in the ADC role in my opinion. What I mean is she has high damage, and you have the potential to outplay other players and get kills or live when you otherwise would of died if you played another ADC. This is why I like her.