If you are comparing one seo company against another, the things you must look at are sheer effectiveness across the client list, as well as how long it took to achieve the goals that were specified. Except for the potential using of techniques that are outside of the scope of what is allowed by search engines, the only thing you need to worry about as far as one seo company versus another is the actual achievement of the goals they were contracted to work towards. SEO is different in every case, and the types of work that must be done for one client will almost always be different for another client. Additionally, the effectiveness of the program will have more to do with how well the company can figure out how to adapt to the competitive landscape than the actual specific tasks involved in the daily work. This is because SEO programs are designed to boost rankings among competition, not just build links or create content.