stock trade broker

What online broker that offers the highest interest money market while in the cash position?
What I am trying to say is that when you just sell a stock and cash position, and you want to get a good interest while you are sitting there to wait the next opportunity for the next stock, which online broker (Fidelity, E Trade, Ameritrade, Schwab, Scottrade, etc) is better at interest in cash position?
I would be careful here chasing performance. Many of these money market funds are asset-backed commercial paper found by a few notches above mortgage-backed securities. None of them has broken the ball (yet), but a very few bond funds have short-term flown, and no Chinese Wall between short-term bonds and commercial paper.
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