I gave better plot to B5. It had a story to tell from the start and it told it. I like DS9's plot very much but there is no question that B5 was planned, and I enjoyed that.
For cast, there is no doubt in my mind that DS9 had the better cast, there were some real stinkers on B5. That said, B5 did have Mollari and G'Kar, and Peter Jurasik and Andreas Katsulas alone are able to elevate the acting to the point where I voted for both shows in this category
Sisko get the nod for better hero. I'm not a fan of Sherida, I preferred Sinclair.
Dominion gets the vote for baddies, Jeffrey Combs as Weyoun is fantastic and you have to count Marc Alaimo as Dukat and Casey Biggs as Damar in the baddie camp and there is no question that these three characters, portrayed by these three actors are more compelling antagonists than wavy shadow spiders.
So, B3 = 2, DS9 = 3.
I love both these shows!