So I've lost a ton of Elo learning to play AD carries and in particular I am horrible with Corki. That said I didn't realize how nice the Ashe buffs were a few patches back, outside of one game where a 4-0 Renkton started jumping me, she's quite a strong champ (still won that one but was 9-8-8 (way too many deaths).
Corki is such a horrible AD range champ in my opinion. I've stated that here before. No real burst damage, no CC, and no real steroid. His gatling gun is clunky to use in a team fight and puts him real danger to do so. He is OK for a poke comp team, but he is too easily caught even with Valkyrie to use as an escape. Except for his ult, he lacks the range to kite effectively.
Only good AD ranges in my opinion are one of the following.
Caitlyn, Graves, Vayne, Tristana, and Ashe.
Ashe is just barely good enough now due to recent buffs. I still don't like her attack animation problems and lack of escape beyond kiting. Also she is way too dependent upon landing her ult.
I also still dislike Tristana split damage on her ult. If it scaled either AD or AP she would be solid if not the best AD range.
Vayne and Graves lack range, but can overcome those problems.
These are the "premier" AD ranges in my opinion. Meaning not picking one of these is hurting your team.
Other AD ranges though just don't stack up for various reasons. Those are Corki, Teemo, Ezreal, Kog Maw, Sivir, Miss Fortune, Lulu, and Kennen.
Some of these in this list are better than others. For example Kog maw is much better than Corki or Teemo in my opinion. He has a steroid. He has massive range. He lacks a good passive. He lacks and escape. He is really slow as well. He also has a longer animation start time to his attacks than I like. His damage is split and he has massive mana problems early to mid game. Because of that he is not what I would call "premier" but he is damn decent at least. I won't complain about having a kog on my team as an AD range unlike a Corki, Teemo, or Ezreal right now. Those three are the worst of the AD ranges in my opinion right now.