Regarding the topic question... my answer is no one. It's kind of an overused trope of two leads getting together. (Or multiple pairs of leads.)
A good candidate would have been Dr. Elizabeth Lense from "EXPLORERS", though.
Side note: someone mentioned that Kira and Bashir didn't have a lot of scenes together. Some examples...
"THE PASSENGER" - the entire beginning was the two of them on the runabout and then rescuing Kajada.
"CROSSOVER" - a lot of scenes in the episode.
"THE JEM'HADAR" - they were on one the runabouts together.
"CIVIL DEFENSE" - in Ops the whole time, along with Dax. And later Garak.
"DEFIANT" - just before Tom Riker greets Kira, they has a whole scene where she lost her patience and he ordered her off duty and relax.
"LIFE SUPPORT" - multiple scenes.
"IMPROBABLE CAUSE" - right after Bashir and have Garak have lunch, they are talking about what an alien breathes.
"RETURN TO GRACE" - the beginning when she is getting her shots.
"THE QUICKENING" - along with Dax, in the runabout.
"APOCALYPSE RISING" - in Sisko's office, and her jokingly saying the pregnancy was 'his fault'. (Clearly, the writers were having fun there.)
"THE SHIP" - Sisko's office, the legal trouble with Quark. Odo was there, too.
"TIES OF BLOOD AND WATER" - multiple scenes relating to Ghemor, including her talking to him about watching Ghemor's last minutes.
And many more.
I agree they didn't have many episodes together, but they definitely had their fair share of scenes together.