I have traded professionaly for many years through a major prime broker using FIX prootocol and executing thousands of trades a day. I have recently done some limited trading at IB using the API and TWS. Given the technolgy offered, in conjuction with very low rates, IB seems hard to match. If you are less sensitive to commissions, there may be other options that are more suited to your needs. If you are a high volume trader, my feeling is that IB is hard to beat. Also keep in mind that few brokers are offering portofolio margining to smaller customers. To match the rates offered by IB (unbundled) at a larger broker you would need to reach much higher volume breakpoints. Thank you.