That depends on your needs...The independent investor is best suited with a low cost provider like, E-Trade, TD Ameritrade, Schwab, or Fidelity. I personally use TD for my clients. E-trade has too many financial concerns and have been trying to make themselves attractive to a buyer for years with no luck. Scottrade is cheap but limited resources. Although they are improving.
If you're not so self directed, you can try the traditional wire house firms like Merrill Lynch. However, in most cases their cost is not worth the service in my view. You're still better off with a TD or Schwab, as they can refer you to an independent advisor who works off of their platform that they have pre screened. They are typically Fee Only unbiased services.
It Really depend on what you're looking for.