Personally I don't think their has to be a case of FX or Indices - I think its more a case of each market (FX, Commodities or Indices) on its merits for the particular system or systems you're trading. For any given market there will be some strategies that work well and some that don't, so its really a case of testing a strategy on as wide a basket of markets as possible to see which ones it works on (or works best on).
