Remember when debating this not to personally attack each other.
IMO its 
shes rarely played and seems to need near perfect conditions for a good gank based on what i have seen. Late game she seems to just be there, but not able to acually do anything.
this is just based from what i have seen
atm kastila in her current state. People claim she's OP but she needs a good support and can't do much on her own.
All champions have their main and their place.
But I think Quinn is the most useless champ. Someone does something in her kit better. and her bird form doesn't make sense for an ADC AND it just doesn't flow at all.
I was trying to think earlier when the last time I saw 
was. He might be up there, along with 
By far the worst!
the worst champion is definitely sion. u taught shen was just a meat tank? at least shen can taunt/ult someone. sion misses every of his awful skillshots and becomes useless.
honestly, i believe it is quinn, her kit is just weak and an ult that doesnt fit anywhere, i use it to get back to lane most of the time
I think GP is still pretty bad
Now that's gonna depend on what you mean by worst. Worst champion at fulfilling their meta role 
, champion that brings the least utility to the team 
, champion that's least capable of carrying a game 
, or many other qualifications of "worst".
Unless any of the above posters are Diamond+ skill level, I don't think any are really qualified to be able to give an accurate opinion. I have personally seen every champ in the league called terrible and "worst", but ultimately it comes down to the person playing it. There is never a repeat of a situation twice. There are too many variables involved in the average game to actually call a champion bad. A "weak" champion is usually a result of basic stats and mechanical relativity.
