If both markets were both liquid and tight markets, FX futures would be better. The future would be one market with the best Bid/offer rather than a fragmented market were your broker shows you the bid and offers from the banks on his platform with a vig added in. Different FX platforms can have different markets. With futures, the counter party risk would be with the futures exchange rather than your broker. If your broker goes bankrupt,you have no protection with FX.