Regina unknowingly made a mistake when she trusted young Snow White with a secret. Not long afterward, Cora killed Regina's true love, Daniel, and Regina swore to get revenge on Snow White ever since. This is the conflict that Once Upon a Time is most reliant on. The relationship between Snow White and Regina Mills was the dynamic that made the show what it was. However, it was not the only rivalry to grace the streets of Storybrooke. From long time enemies Rumpelstiltskin and Captain Hook to Regina versus her other half, there were conflicts all over the series. While some were dynamic and held years worth of history, others felt like they were there for the sake of conflict.
BEST: SNOW VS. REGINA
Regina's confident stride that breaks up Snow and Charming's wedding was the perfect set-up to explain their relationship. Things had not been good between them since briefly after they met when Snow White was a child. Regina's curse, while torturing nearly everyone in the Enchanted Forest by bringing them to a land without magic, had been designed with the intent to keep Snow unhappy forever. While Snow attempted to reach a hand out to Regina to make peace, things never worked out that way until a while after the curse had broken.
WORST: REGINA VS. ZELENA
In season three, Once Upon a Time introduced a new antagonist into the fold. She walks into Regina's life during the forgotten year. At first, known as the Wicked Witch, Zelena informs Regina that they are sisters. Zelena wanted revenge on Regina for being everything she wasn't. Regina had been raised by their mother Cora, and later taken under the wing of Rumpelstiltskin. Meanwhile, Zelena had been sent away from her family. She is found and brought in by a woman who wants her and a man who hates magic. While their rivalry eventually grows between them personally, its beginning has more to do with Cora's choice to send Zelena away.
BEST: EMMA VS. REGINA
Emma and Regina had every reason to hate each other when they met. Emma was concerned about Henry and how he described Regina's parenting style. Meanwhile, Emma was Henry's biological mother and a threat to Regina's relationship with him. After discovering that the curse is real, Emma faces Regina's actions toward her parents. Their rivalry is one of the best because while it does include Regina's past with Snow and Charming, it is also heavily based in the present and how to handle co-parenting Henry. Early on, it was entertaining to watch the two attempt to outsmart each other.
WORST: EMMA VS. GIDEON
It was Gideon's job to kill Emma Swan. However, Gideon was not in his right mind during any of this. Gideon was only a pawn in the Black Fairy's larger plot. He had grown up under the Black Fairy's thumb watching as she tortured children. The Black Fairy decided that to get the job done she had to steal Gideon's heart and command him to do what she wanted. Given that Gideon did not have a say in what he was doing, their rivalry did not count for much. During their last standoff, Emma decides against killing Gideon, and he is returned to being a baby.
BEST: REGINA VS. RUMPLE
As two of the most intelligent and manipulative characters on Once Upon a Time, when Regina Mills and Rumpelstiltskin were on the same side, they were a terrifying match. However, they were just as dangerous as enemies. When on opposing sides, Rumple and Regina had a way of using magic and manipulation to get the other to do what they wanted. However, watching them outwit each other was like viewing an intricate and carefully thought out game. In the end, their relationship had gone through so many stages that they understood each other better than anyone else.
WORST: EMMA VS. THE BLACK FAIRY
With the book coming to an end, it was expected that Emma would face the final battle. Gideon's arrival in Storybrooke is only the beginning of the Black Fairy's plan to kill Emma. However, those plans were more ambiguous. She sees Emma as an obstacle to move past. There is not anything personal in their rivalry that keeps the plot moving. They do not have any type of history that justifies their dynamic, and instead, it makes the final battle come up short. Emma's last sword fight is against Gideon after Rumple killed the Black Fairy.
BEST: RUMPLE VS. HOOK
Of all the rivalries on Once Upon a Time, this one was certainly the longest. Lasting for centuries, things initially went wrong after Milah fell in love with Captain Hook. Wanting a life of adventure with a confident man, rather than the coward she considered Rumple to be, Milah was the reason the two men became enemies. After becoming the Dark One, Rumple returned to Hook and Milah's life one last time, and when the fight was all said and done, Milah was dead, and a life long rivalry had officially begun. Even after both men had moved on from Milah, she still influenced their dynamic.
WORST: WISH RELAM DARK ONE VS. RUMPLE
While Rumple versus himself could have been an excellent rivalry to prove how much Rumple had changed, Once Upon a Time squandered the opportunity in its last season. The final villain of the series turned out to be the Wish Realm Dark One, who had gone his whole life without knowing what it felt like to be in love with Belle. Instead, he only knew the bitterness of what it had felt like to lose Baelfire. Wish Dark One's scheme felt out of nowhere and Rumple did not have enough time with his alternate-self to dive into the issues the finale presented them with.
BEST: REGINA VS. EVIL QUEEN
Regina's decision to split her evil self from her good causes mayhem all over Storybrooke. As the Evil Queen had not been destroyed, and without Regina's re-built conscience, the Evil Queen has nothing to stop her from going after Snow White. Regina's internal conflict became a physical one as she had to figure out a way to defeat the worst parts of herself. Finally given a chance, Regina realized the best way to beat the Evil Queen was to accept the dark parts of herself. Giving the Evil Queen some of Regina's light, both versions of Regina have light and dark inside them.
WORST: DRIZELLA AND RAPUNZEL
Rapunzel, also known as Lady Tremaine, was guilty of favoring her younger daughter, Anastasia, over Drizella. When Rapunzel was only left with Drizella, she was willing to do anything to bring her younger daughter back, including sacrificing one for the other. Unlike the dynamic between Snow White and Regina, there is not much history to explain the depth of their relationship. However, the series puts a stop to the chance for reconciliation by killing Rapunzel halfway through the season. Later, Drizella and Anastasia leave Hyperion Heights with a few episodes left in the series. Their relationship hits an abrupt end instead of a fleshed-out conclusion.