Birds of Prey (And The Fantabulous Emancipation Of One Harley Quinn) does a better Harley Quinn story than The Suicide Squad. The character has become a major highlight in the DCEU, and while she has a great showing in the latter film, Birds of Prey remains her best.
Despite the DCEU's early rough days, Margot Robbie's Harley has been a huge highlight since her debut appearance in David Ayer's Suicide Squad, despite that film's overall poor reception. As such, she would go on to star in Birds of Prey and The Suicide Squad. Throughout each film, she goes through a character arc that gradually transforms her into a better person, to the point where it can even be said the DCEU has turned Harley into a full-blown hero.
While neither Birds of Prey or The Suicide Squad is technically a Harley Quinn movie (as they primarily revolve around the titular teams,) both of their stories feature the character in heavily prominent roles. In particular, her role in Birds of Prey is what very much makes her the star of that film. While her part in The Suicide Squad is great too, the film's unpredictable nature surrounding the other characters makes her a bit of an odd fit. The film is incredibly indiscriminate about which characters are killed off, but Harley's icon status makes it clear that she won't die, which undercuts James Gunn's original assertion that no one is safe in the film. The arc she gets in Birds of Prey is what helps establish herself as a mainstay in the DCEU.
Birds of Prey shows Harley breaking up with Jared Leto's Joker. The character has always been defined by her relationship to the Clown Prince of Crime. However, due to Leto's divisive portrayal in Suicide Squad, the DCEU has gradually shifted away from him. This allows Harley to come into her own as a character, breaking away from solely being Joker's companion. Along similar lines is her taking in Cassandra Cain as a protege while protecting her from Black Mask. While it doesn't necessarily redeem the character for her past (and current) misdeeds, it highlights her sympathetic nature and perfectly foreshadows her more heroic turn in The Suicide Squad, which is paid off by her killing President Luna for planning to feed enemies and their families to the DCEU villain Starro.
Both Birds of Prey and The Suicide Squad help Harley Quinn tremendously. The former film, however, delivers a better story for the character. Still, she currently has one of the most promising futures in the DCEU and has these films to thank for that.
