I voted Ezri - most of the others I would say are either quite well rated (Quark, Bashir) or justifiably obscure (Neelix, Travis). I thought Ezri was a great character and well acted, a young lady trying to come to terms with the gift of a symbiont she never asked for. Her interactions with the other cast members were wonderfully done, especially when she'd say something from Jadzias memories that was meant to be comforting but which came across weird and morbid. But I never thought she got much credit at the time, mostly she just got complaining that she was taking up too much of the final season with her introduction and focus episodes.