Best Ranged AD Carry?

All I've ever heard is Vayne, Ashe, or Caitlin. I see how Vayne is good, but Caitlin seems to fall off for me and I cant play high damage Ashe for the life of me. I see Tristana (if not Graves) as better AD carries. Trist has more range and better farming. Who is the best ranged AD carry and why?