Firstly, it may help you to understand the difference between direct access and the non direct access brokerages, and secondly, the difference between using a browser-based trading platform and a stand-alone platform.
Other than that,
Brown & Co. over a certain amount of shares commissions go up;
Freetrade pays for order flow, as do most other browser based brokerages, like Scottrade;
IB waives market data fee if you have more than $30 commissions in a month;
I believe Ameritrade has a guarantee of best fill (you don't mind looking up the time and sales with every trade?).