I am with IB now but I used to have accounts with Scottrade, Ameritrade, TD Waterhouse, Datek, TD Waterhouse canada, Etrade, Fidelity...
I was with them for more than two years and and with some over 5 years.
I can not compare IB with any of them. IB is far far a better broker "For me". I like their strict liquidation rule. I like their low margin rate. I like their commission rate on options, stocks. I like their paperless policy to reduce costs.
I have been with IB for 4 years and I called them once that I got my answer. When I trade a stock, I have a plan to short 2000 shares at 40, I don't need to do it once to get lower commission, I do it 200 shares at a time to test the water and sometimes the stock goes up, I short at higher prices that compensates the commission cost. If I were trading always in 3000 to 4000 share blocks and over one million shares a month , I would go with bundled commission rate.
All things said, IB is not for everyone. Some investors might hate IB if they open an account with IB. If you trade 4 times a Quarter and also like to buy mutual funds and you are not in option trading, IB is not for you. Those who join IB, should have at least 2 years of trading experience.