Same Era, different universes, similar genres. Its even rumored that JMS approached Paramount first with B5, got turned away, and then Paramount came up with DS9.
I'm firmly in the B5 camp. The trek universe always felt too sterile, too idealistic. The races had no *depth*. Basically, they had all their own *
hats*. Klingons were Proud Warrior Race Guy, Romulans were all Magnificent Bastards, So were Cardassians (sorta, but they're our friends kinda now), Vulcans were all Spock, Bajorans were Human Lite... etc.
The races in B5 felt more developed to me. Each race had their individuals and one would be less able to stereotype based on appearance. Sure, Centauri were probably all backstabbing bastards, and Vorlons were all enigmatic zen masters, but they were individuals.
Tech wise, B5 was a *harder* sci fi than Trek. Space combat was more realistic, no gravity in space, no *dogfighting* per se. "Lasers" for the most part behaved as lasers should. Ship to Ship combat was generally at close range, as missile defenses seemed pretty effective. The bad guys were scary and believable for the most part. The Shadow Menace > The Dominion
Sheridan could captain rings around Sisko. After all, Sisko was the Chosen one! (The Sinclair Equivalent
)
Ivanova > Major Kira
Garibaldi > Odo
Franklin < Bashere But Franklin was more human (if that makes sense)
Lyta > Dax > Talia... And there, the comparisons kinda break down. There weren't really any "Ambassadors" on DS9. There's no Quark on B5, nor are there Jakes or Noggs or Quark's useless brothers. Which, is really a good thing. To me, they just felt like forced comedic effect guys. (Ferengi have the "Greedy" hat.)
As villains, the Shadows > *. Psi Corps > The Cardassians
Emotionally, the B5 series was more gripping... Hard to describe, but DS9 never really pulled me in. I gave it something like 2 seasons, but I never was as enthralled with it than B5.
But, as this is Wankery at best, I'll stop here and just say B5 > DS9.