I have both. Regarding strictly brokerage, I have found IB always better for quote speed (stock and futures, but supposedly TS will soon have a direct quote line to speed up futures), faster exect., and cheaper. However, TS's analysis package is very good, been using some form of it for 5 years.
Forget about TradeStation. It's a PDT-killer whore. Also it has higher minimum account balance and initial deposit requirement, 10K and 30K for non PDT and PDT respectively. Way to go with prop now. But TS has just a little less stricter definition on PDT, 4 day trades in 5 business days. Hey, should I report them to the NASD in the hope to collect some pathetic rewards.
Think logically about it. Who is the better candidate: Someone who delves into the brokerage service after specializing in system development for years, or a firm that devotes all its resources into offering an efficient comprehensive brokerage product? Use tradestation for backtesting (it's specialty) but IB for execution of your systems.
I also use TradeStation for the platform, and keep a minimal (5,000) amount in it to get the $109 per month fee. And trade (non-day) expensive stocks with the money to keep it active and commissions low. IB I use for futures and stocks. Price is right and execution is great. Get the best of both worlds that way.
For me Tradestation is an easy choice. I think where Tradestation shines is in Strategy testing; I can't imagine anyone putting their hard earned money on the line without properly back testing their ideas. I believe as others mentioned TS did have some problems with their datafeed, but that is being resolved. The newer version of TS due out in March will have many new features along w/ automated futures trading and integrated futures order entry. I have not traded with IB, their commission structure does look better than TS. I guess if you really wanted to trade with IB a eSignal + IB combo may work or Wealth Lab + IB may be good. However based on various threads I have read, I think TS customer support is much much better than IB. I would highly recommend TS, especially if you are a new trader w/ less than three years of trading experience. TS is very user friendly. Good luck Trading.
It is easy. Piece of cake. Just maintain over $100K in *both* accounts, and then you will never have to make a choice.