I think the hostility Kira showed Quark was a bit of Odo inspired keeping him on his toes. I think also her position as first officer meant that Kira had to be a hard arse to Quark considering some of the shenanigans he got up to. Sisko didn't seem to fond of him at times either, but they were all there for Quark when he lost everything to Brunt.
I never really got the hate towards Keiko. I felt like Keiko and O'brien's relationship was pretty realistic. I also thought Jadzia and Work worked well together.
Overall i think DS9 did relationships the best out of all the trek series.