I do some Forex trading through TOS/TDA - I have been very impressed. I pay the commission wish ensures a tight spread. TOS/TDA has a perfect regulatory record. When comparing the live quotes with Oanda they are in synch - sometimes TOS/TDA is slightly better. Last time I checked they passed the orders to Gain Capital.
Us Fx traders like the flexibility - can size positions as we want, have many more currencies to trade, no carry costs like you have if you have to roll a futures contract. Forex is a much larger market with incredible liquidity. As a primary futures trader Forex complements my currency trading.