They have the lowest rates that I've found and their execution is excellent. If you are a beginner investor their platform can be somewhat intimidating however as it does not have as good a user interface as say an E-Trade. However for the active trader it is an excellent broker. I do close to 100 trades/month so for me there is no comparison. Cost is around $1/trade and options is even less. Can't be beat for the price.

IB is the choice for professional traders and institutions.