I like both but B5 S1 was trying to change the presentation of science-fiction on television, as well as showing how TV narrative could be drastically different to the current norm. DS9 S1 was just.... TNG on a spacestation and while I really like Emissary and Duet, there's nothing as good as Signs and Portents or Chrysalis. You could skip DS9 S1 and miss pretty much nothing whereas B5 S1 is way too vital to the overall show. Soul Hunter isn't amazing but contains solid backstory and foreshadowing, whereas something like Q-less is just an utterly pointless watch.
DS9 is one of my favourite shows but B5 is one of my favourite stories
. There's just a lot more to it. For instance, the war between the Vorlons and Shadows comes down to an interesting philisophical conflict whereas the Prophets vs Pah-Wraiths conflict comes down to 2-dimensional, cookie cutter Good vs Evil.