I can't vote on this, since I haven't seen all of Farscape yet (I'm working on it), but I absolutely love both shows. As space opera on television goes, I think they're about as good as it gets. Both have their weaknesses (for instance, they both took a while to find their groove in the first season) but the good points more than compensate.
I love B5 for the dramatic storylines, political intrigue, mythology and down to earth vision of the future. I love Farscape for the fantastic, evolving relationships between the characters, the humour and the delightfully screwed up storytelling. And I love both series for their characters.