I would recommend to consider the following elements to provide reasons on why you should consider a particular company:
- Sectors of interest: specific focus of the company in areas/products interesting for you
- People you met and culture: specific people of the company you discussed with, and the things they shared on the company
- Your growth opportunities: specific programs of the company you heard about to enhance your growth
- Company potential: how much the company grew in the last year, which is a good guarantee for your future career as well
- Size/reputation of the firm: smaller companies usually offer a more entrepreneurial culture, with higher growth potential internally. Bigger companies have more resources and support staff, and more prestige in terms of exit.
You may choose the three points more relevant for you and structure your answer accordingly.
Whatever topic you choose, you should apply a simple rule of thumb: if you can substitute the name of the company with another and have the answer that still makes sense, it means your answer is not specific enough. To be specific, you should talk about growth rates/specific people you talked to/specific research paper you read on the company. Yes, it will require some time spent to prepare this question in this way. But will also allow you to stand out, as very few people invest time preparing on this.
Hope this helps,