Is there a vote for none, again no champion is OP, no champion is hard to play against. You have to learn how to play with fundamentals first. 6 champions to explain how to fight against each one. man that is a lot of info to dump onto one person. if it were one question like how to fight against Senna, then players could break down how to engage into her and counter. I will do my best to explain how to fight against all 6 champions.
First thing first, you win and lose through the draft people.
Lesson one, if you are 1st pick or 2nd pick in draft there are safe picks aka champions that are safe to pick for your role.
IE for mid for example safe picks if you are 1st-2nd are Ori (phase rush), Vlad (phase rush), Fizz, tali, Neeko (Glacial), Leblanc, Ekko, Twisted fate, Annie, Ahri (glacial).
Also again all roles have safe picks for their respective assignments.
Pick 3rd and 4th if you can counter or have synergy with your teammates pick your appropriate champions or one trick it.
(side note all players should have 2 roles they like to play IE, MId-Top, Jungle-mid, bot-mid, Support-adc, support-mid, Top-mid,) and vice versa,
also be sure to have 3 champions that you feel you've mastered, or just love, love to play. And or One trick it but have a 2nd champ in the pocket too.
4th pick or 5th is great to simply counter your opponents lane champion. Use two monitors, have second website open or run a 3rd party app to help you grow your mental library of champions to counter your opponents champs (but this is more high elo) or plat and above from what i've seen.
Some gold players and above understand to select counter champs to their laners, but mainly silver and below players dont have the knowledge yet. or any fundamentals yet.
Shaco ---is just sweepings lens, and imagine shaco is a closer, if your teammates or you are low on health he is going to engage and finish a teammate or you. when he fights have sweeping lens ready and control wards ready or just wards ready, you can immediately place a ward on your body where you are standing to kind of cheese an auto out of an enemy champion. Think of a ward like a totem.
Shaco--= peel engage, read and react and disengage against him then sweeping lens, focus fire with 2 teammates and having CC is a must or enemy champs that can interrupt knock up shaco. Shaco is all burst damage, some fear, and can really only have short trades. so sustain champs poke champs, control mages, and champs with interrupt knock ups can finish him, what does shaco excel at killing artillary mages, burst mages, ADCs, and enchanters, and some slayers. shaco will kill champs that dont have good mobility or champs that cant sustain through his burst, shaco is basicly good against those champs that i listed that dont have CC. Shacos worst nightmare, control mages and vanguard tanks.
Ekko. ---is also short trade, all in burst ap assassin.
Ekko cannot sustain but has excellent mobility so you have to dodge his que, interrupt knock up, and counter his champ. with a control mage.
Ekko excels at killing adcs, and the same targets that shaco can.
Sett,-- - is a sustain juggernaut, so he wants long trades to proc his passive his grit,
short trades and read and watch his grit meter to poke him, burst him, and engage then walk away.
sett is also another champion like garen different kit but easy to learn and easy to play against.
find champs that counter juggernauts like Illoai, Maokai, Poppy, also Sett is designed to kill slayers and ad bruisers,
he is the direct counter to those champs as well anay juggernaut is a direct counter to ad bruisers, remember ad bruisers want to fight and need to fight so playing as sett you want to force opponents to build up grit to then use it.
again CC , interrupt knock up and other vanguard tanks and poke mages can mess up Sett.
Fiora --- same concept, she is an all in ad bruiser, i believe shes a slayer off the top of my head treat her like Yas,
CC, poke mages, glacial mages, interrupt knock her, If i see a fiora top, i just vanguard tank to counter her, IE, poppy, ornn, maokai, Sion, malphite.
or GP, or Vlad, or Ryze top to counter her.
but if you want to trade blows then pick another ad bruiser to go for the boxing match, like Aatrox, Riven, yas, (etc...)
id rather love to have the counter pick, then to match punches with her.
because when you counter your enemy laner, and you are good enough you will end up in better 1v2 situations. (when I killed a fiora and master lee when they tried to gank me and im playing Maokai, :P ) but again, wave control, dodges skills shots, and weaving attack animations and canceling attack animations are apart of the fundamentals to players need to learn) macro>micro.
I dont think I've ever lost against an Aphelios hes an ADC.....
like any adc what do they lack mobility so same principals apply.
check proguides youtube, https://www.youtube.com/watch?v=3vwrE8k68Qw
this is "The ONLY ADC Macro Guide You'll EVER NEED - League of Legends Season 9" also applies to season 10.
Enjoy.
Senna..... same concept, shes like Jhin or caitlyn, long range adc. You can either control your waves, maximize your range and wave clear proper, pick MF cait, jhin into Senna, or duo q bot lane with a support friend, or have your friend that is a midlaner play support with you with good comms, and communication synergize your bot lane combo to match or beat your opponents. check out CoreJJ macro guide to the bot lane, so much great info for ADC's and supports to use.
best of luck on the Rift, good luck in season 10.