A custom web design is one designed keeping your business fully in mind. It's the classic process of optimization, but not only for the search engines but also for your visitors. These are important factors of the process, but they are not the parts that have to do with making your website unique. A truly original website is one that is optimized for your business.
If you are aiming at creating a unique online identity, then templates are not an option. Web templates may be visually impressive, it may even suit your business nicely, but it is not designed specifically for you. Adding your own text, applying your own graphics, does not fix the limitations of a template. This doesnt necessarily mean that a template cannot make an effective site. It means that a template cannot make a custom web design. For that, you need unique graphics. You need a layout intended for your audience. You need a linking structure that suits the structure of your business.
For a presence optimized for your business, you need a professional web designer. This is important, because there may be web design firms who offer templates which can be impressive, with their variety of easily adaptable layouts and designs. If, on the other hand, if you want a custom web design then you should take advantage of the skill and experience of professional web designers. Naturally, it isn't as quick; it isn't as cheap. But the benefit is having a site created with your specific business in mind. The goal of custom web design is to give your business an on-line personality, and to make it exactly the personality that you wish to convey to your visitors.
Custom web design is the way to go if you really want your business to shine online. Templates are great for a quick fix but a personalized design makes all the difference in capturing your unique brand identity.