I would describe myself as unique, different, happy, confident, and even a little short tempered sometimes. But if you ask other people about me they might say something different. Honestly it depends on the person you are asking and how long they have known me.
You need to back up these points with relevant examples of where you have demonstrated these. This question may be phrased in different ways such as “How would your best friend describe you?”, “Why should we take you rather than the other applicants?” or “Tell me something about yourself”.