It's easy to argue that "Blue Bloods" favorite son Danny Reagan (Donnie Wahlberg) has had a pretty charmed professional life. He's been a lifer in the force, having only taken off a bit of time to serve in the Iraq war. He's received a number of promotions and is among the most trusted cops on the beat. Sure, he leads the force in complaints, but he also leads his unit in collars, so he's good at getting the job done. If you want to be a successful cop, you've got to break some eggs — in Danny's case, that has meant losing his house and his family getting endangered. And indeed, it's his personal life — complete with PTSD, a dead spouse, and two sons he's raising on his own — that remains messy.
Currently helping to keep his professional life more competently ordered is Maria Baez (Marisa Ramirez), Danny's longtime friend and his partner on the force since 2013. Lots of fans love their partnerships and think they ought to combine households. But believe it or not, Baez isn't Danny's only professional partner — and for many, she isn't even the partner they'd most like to see working with Danny.
Outside of Maria, Danny's longest-lived friend on the beat is Jackie Curatola (Jennifer Esposito), who stuck with him from Season 1 to Season 3. Their matching personalities and her ability to call him out in his worst moments make them an interesting duo. It's a topic that fans of "Blue Bloods" aren't afraid to be passionate about when they try to decide which of Danny's several beat partners is the best. in fact, fans posting to the "Blue Bloods" subreddit actually think Jackie is Danny's perfect match.
While Maria Baez and Danny Reagan have opposing personalities, with her personal approach clashing with his more serious, by-the-book way of looking at things, Jackie Curatola and Danny's partnership was overall more no-nonsense due to their similarities. Jackie doesn't often call Danny out, which means they're often focused on one single, similar goal. Maria challenges Danny, forcing him to occasionally correct himself.
With Baez and Reagan, more often than not, that results in a partnership that sees them butting heads and really arguing about what's right and wrong in a case, something Jackie and Danny almost never do, as the twosome share a sly sense of humor and ethical working style. Outside of work, Jackie is a much lonelier figure — divorced and without the strong support unit the Reagans offer one another, meaning she needs his support even more off-duty. Yet they never get quite as close as Maria and Danny have, with the latter twosome preferring to form a strong unit against the outside world (and their phalanx of terrifying enemies) with their friendship.
In fact — perhaps due to his close relationship with his wife Linda (Amy Carlson) — Danny didn't often mix up business and pleasure when it came to Jackie, and she wasn't a frequent guest at the famous Reagan family dinners. At least Maria's been to a few during her time on the force.
On the other hand, the fact they have a lot of similar traits doesn't mean Jackie and Danny didn't have chemistry as partners. Fans down at the "Blue Bloods" subreddit definitely enjoyed Jackie's presence when she was with the show for that reason. "I was bummed when she left," said u/Responsible_Candle86 in a post about Danny's many partners. "Jackie [complemented] Danny as a partner. They are very similar in personality so they pretty much flow well," said u/StevenArviv. In fact, several fans posting to that particular post were shocked that Jackie was not an option mentioned by the show's OP.
And then there are those who definitely support the two of them as a romantic twosome. "I always shipped Danny & Jackie. They had such good chemistry together," said u/AllysCrossing in a post that compares Maria's virtues with Jackie's.
While Jennifer Esposito has since moved on to other roles and Maria is definitely Danny's favorite friend at the moment, the door was left open for Jackie's possible return. She did, after all, leave the force because she was showing signs of stress due to the high-pressure nature of their jobs. Perhaps someday Jackie and Danny will encounter each other, even if that means they're on opposing sides of the badge.