To earn top placement your pages must be optimized for the engines. AOL and MSN produce the greatest traffic with Yahoo in third place. The other engines follow at a distance. The first and foremost measurement of a successful web design firm is the extent to which they support their clients after they have completed the web site. It just can't be done without follow up monitoring and constant refinement of the site.
Reports showing the search engine positions are an absolute necessity.
If they don't have these you can assume that the sites they create will not draw significant visitor traffic. So, don't be mis-led by fancy web sites and even fancier sales pitches. This is the only way to select a company that will create a profitable web site for you.