Its confuse me some time what is different between facebook page and group. Which will best for my needs.
I'm sure you should create facebook fan page. It is good for business because it has listing in general list of pages. You will have ability to create custom landing pages using FBML application to convert your visitors( you might try to use facebook fbml templates). Facebook pages has unique and seo friendly URLs.
I think it totally depends on the way you want to promote your site. The group you create will have a proper conversation chat and you can even add some good pictures every day or once a week and start some interesting discusssions. On the other hand, for a fan page you can have a landing page under the option FBML to attract more people you visit your fan pages and direct them to your site.