Perhaps look here where "Among individual performers, Interactive Brokers (IB) once again took the top spot among major brokers as it had the highest amount of active traders as well as accounts being the most profitable." http://forexmagnates.com/exclusive-q1-2014-us-forex-profitability-report-fewer-traders-more-profits/
I have three forex accounts and trade Currency futures, often times one of the forex dealers will have a discount or prem compared to futures, I think this was a no brainer to me to trade this way especially since I scalp. But when I put on a long term trade rather go with Futures Broker as it is cheaper if not at home, calling the broker to make the trade, easier to get a hold, and he actually knows me. Just concentrating on tight spreads is not always cheap, if the site freezes and you have to reboot, how much will it cost for you to call to get you out? Just one occurrence can wipe out a months' worth of the spread difference compared to another forex dealer, so this has to be considered as well. Just way too many have a couple grand and open accounts thinking they will become one of the 1%ers with very little education and study.
I do wonder if the % profitable stats is biased towards IBKR because IBKR has more professional traders as opposed to OANDA which would attract more pikers. Not exactly indicative of an "edge" provided by a better broker. Nonetheless, I remain a customer of IBKR.
So you're telling us you sit there and arb OTC dealer cash vs. futures? I'll give you $10k today if you can show me a run from this week (prior to the stamp on this post) with a single arb fill (cash and futures).