Due largely to the fundamental difference is how the two shows were handled (B5 generally laid out in advance, DS9 improvising to a large degree), I don't care to compare the two in that manner.
Cast-wise, they both had their strengths and weaknesses, so again, I don't feel there's a good basis for an overall statement. I'm gay, but a Kira-Ivanova fight would be gangbusters.
Sheridan probably beats out Sisko for speechifying, but Sheridan may have been a bit too much of the Ideal vs. Sisko's Realistic (we're all well-aware that he was willing to get his hands dirty).
The Shadows (well, their ships) were the major reason I got into B5 initially, but as a threat they're vaguely simplistic (EVIL!!!) compared to some of the dynamics of the Dominion...nevermind that those dynamics never got to the point of fundamentally altering the direction of the story.
I call it too close to call.