I am using Tradestation at the moment. I like the fact that it has viable charting, backtesting, real-time data, historical data, and brokerage all in one. Also, you can use it on Saturday unlike IB. This makes it a compelling package for strategy development / simulations. As always there are other options that can be better, but I've found it the most useful at this stage. I also really like my client services agent, he's been really responsive and helpful. That said, for the very limited trading I actually do, I use IB (forex) which has been rock solid (just doing some weekly trades, so haven't needed a front-end like Ninja for it).