Alexander Siddig was excellent on DS9 in terms of his acting skill. He even played Bashir three different ways as the writers changed his personality twice (not including the Mirror Universe version)! I would like to see how well the rest of the cast could play four versions of the same character.
I just never cared for Siddig's portrayal at all. The episodes that feature him predominantly are the ones I'm most likely to skip over (the story where he ages at an accelerated rate really sets my teeth on edge). Whatever acting skills the guy possess (which I'm sure he has in some measure because he continues to get at least limited work) just didn't gel with me.
I did like Bashir's evolving friendship with O'Brien but otherwise wasn't that interested in his character.
Like I said earlier, I also was sometimes distracted by acting from Visitor and Brooks. But I did actually enjoy their characters for the most part so maybe I remember them in a fonder light.
Siddig has had the most high profile roles of all the DS9 regular cast at this point though, I think.