I am an active trader and I can tell you that Interactive Brokers has MAJOR customer service and accountablility problems.
I have bought stock through them where their trading screen has beeped on the buy execution and has displayed the owned shares on my screen and has shown the shares being as being sold when I placed a sell order - only to be told by Interactive brokers that the shares were never bought or sold. They refused to acknowledge their eff-up and refused to compensate me from my lost profit.
I have placed orders with them to cover at "market" through their "Smart" system and then have watched as the stock runs higher and my order only executes after I call customer service and a profit has turned into a loss. Again IB refused to take responsibility and instead blamed the exchange to which THEY had routed the order. I could go on and on.
The measure of a good brokerage is how they handle their eff-ups. Interactive Brokers seems to have a policy of "we'll take whatever we please out of your account because we already have your money". Also, you cannot escalate problems through management as their management does not acknowledge correspondence.