According to CFTC Feb 06 FCM report, Oanda is the biggest Forex broker in the USA. http://www.cftc.gov/tm/tmfcm.htm?from=home&page=mktfcmcontent
Interactive Brokers offers FX and has much larger capital base. If you're talking US regulated brokerage companies who only offer one product - FX, then it looks as if you're correct.
Afaik featureless Oanda platform is no where close to IB TWS(except for having charts), i don't understand for what reason some retail traders still using Oanda, considering pip spreads being same today for both companies, with IB giving other extra benefits
i think a lot of ppl just prefer to have a platform that allows them to trade and monitor positions rather than general exposure. Admitedly you can get add-ons for tws but the whole system of an api via sockets is laughable (although I still use it, call me cheap but I don't want to pay the extra charge to connect direct to the servers that most other brokers offer for free). IB just needs to sort out a dedicated fx trading section and perhaps add a few more pairs and they'll be difficult to beat
Equally (if not more) important, IB needs to reduce its Ideal Pro rollover costs to offer a competitive FX platform. http://www.elitetrader.com/vb/showthread.php?s=&threadid=64052
IB is very good. So is hotspot. But for smaller accounts ---Oanda is very good as well. IB double margins for cross rates (it margins each leg). But IdealPro is well put together. It is however for larger players. Smaller players are better off at Oanda (especially if you are holding positions). IB is coming out with a position tracking module. The rollover costs can be confusing if you are not used to Interbank (IB has done some of my positions correctly and some other positions that left me guessing----but nothing as of yet to make me jump up and down and start a flaming thread on IB).
The one thing I like about Oanda's net capital is that unlike FXCM (fluctuating more than 10mio up and down monthly), it is so stready and stable... I don't know what is going on with FXCM's net every month. Should I be suspicious about their business model? Maybe it is true they trade agasint their client's position for profit and their dealer didn't do very well in Feb.