At the time I disliked Kira and Quark. Now, I like the way Kira was at the beginning. I wouldn't call it 'Over the top', she seemed just like the situation she came from. I liked her in later seasons too but I do think she moved a bit too far toward the center. At the end she was basically a human who aside from the nose you couldn't tell apart from the Starfleet crew.
With Quark, I think it took the writers a little while to realize he was an intelligent businessman capable of defending his position instead of the cartoon character the TNG Ferengi were. But even at the start he was a crucial ingredient.
Dax, eh, how much can you really change after living 300 years? Along with Quark she was one of the better comical elements in a show with dark enough storylines to absolutely need them.