Great question, although that is a very subjective answer. Many firms these days have access to the same tools, resources and information. What is important is finding an AGENT that is the best to work with for your needs. We all specialize in something a little different - trustee sales, investors, first time home buyers, retirees, etc. It is best to identify your needs and find somebody whose experience and personality are the best fit for you. You are working with the agent, not their company :)
(I will toot Mainstream Real Estate Group's horn here for just a moment: While we are a smaller firm, we have more flexibility in fully addressing our clients' needs well outside the box of corporate rules and guidelines. We do of course adhere to all local, state and federal laws but have more freedom in the ways in which we serve our clients).