Ameritrade, Datek, Discover, E-Trade, Schwab, Suretrade, etc.

On a typical trading day they are all adequate. But the question is:

Which one will perform best on the busy trading days?

What would happen if the Dow dropped one or even 2,000 points?

Every investor out there would be logging on trying to execute a trade. Which one could handle the most traffic? That should be a primary concern.