In her civilian identity, Haruka is easy-going, playful, and even a little mischievously arrogant (with Michiru having to scold her enough to keep her in line). She's extremely protective of those she considers dear to her, often feeling deep regret when she ends up hurting the ones she cares about. Haruka is also somewhat of a tomboy, to the point where people typically mistake her for a man. Michiru explains in Act 31 that Haruka is both male and female, in that she possesses the strengths of both genders. This is likely why Haruka takes on the father figure role to the reborn Hotaru, when she, Michiru and Setsuna decide to adopt her as their own daughter.
As Sailor Uranus, she can come off as being rather cold and extreme. She takes her duties seriously and will stop at no length to accomplish her missions. She doesn't hesitate to kill or attack her potential allies if it means she's able to complete her mission without dragging anyone else into it. While Sailor Neptune generally shares her cold nature as a warrior, Sailor Moon and the other inner senshi tend to oppose her methods, as they would rather find a more peaceful means to achieve their goals.
As a soldier, Sailor Neptune comes off as being cold and distant... much more-so than Sailor Uranus at times, as she is often the one to remind Uranus of their mission. Although it pains her, she will sacrifice whatever is necessary to complete her mission in saving the world, even if it means murdering an innocent girl. This often puts her at odds with the inner senshi, who do not agree with the extreme methods undertaken by herself, Uranus and Pluto.
In stark contrast, Michiru is elegant, polite and sophisticated. She is kind to her fans and is a very loving motherly figure to Hotaru once she, Haruka and Setsuna decide to adopt her. Her personality very much resembles the oceans she has power over, as she can be quite calm and serene... but very scary when angered! She takes pride in her position as a violinist and a fashionista; she has incredibly high taste, expensive hobbies and comes across as being more mature than her actual age. She's a perfect complement for the more masculine Haruka.