Just my sole opinion...
Oanda and FXDD are both generally highly regarded brokers and haven't really had any problems with them, however I will disclose I haven't actually traded extensively in Foreign Exchange, mostly only the ocassional trading as I am still testing the water on both platforms.
With FXDD, I believe when you go sign up a trading account with FXDD Directly, they will give you a choice of their own FXDD trader or MetaTrader and as such I believe you do not need to go through StrategBuilderFX (Aside from that, I will disclose that I feel I have reason to believe that the propriertor of SBFX has possibly been Marketing in other public forums by stealth in order to generate traffic and gain referals (kick backs from either MetaQuotes and/or Brokers they refer clients to), and as such, I am personally reluctant to support SBFX).
When I was earlier this year trying to convert an existing Managed Trading LPOA account with FXDD to a self trade account, FXDD offered me the option of using MetaTrader.
All and All FXDD I believe are alright. Haven't had any bad incidents with them yet. They seem fairly reputable in their business approach, the only bad thing I heard about them was from the manager of a Managed Forex Program I was invested in, telling us to close our FXDD account and move to FXUC. But I feel I have reason to believe that the manager in question had already a long relationship with FXUC and as such was making up an excuse to get people to shift their accounts.
With Oanda, They have their own propriertary trading platform and are based around individual PIP units rather than the more widely accepted 'lots', shouldn't matter too much, but some people take a bit of getting use to this arrangement. Their platform is java based and should work in Linux as well, but the charting tools with in them I personally feel may be a tad too primitive or basic for some traders and unfortunately, (from my point of view) they don't intend to support MetaTrader, Personally I would stay away from their box options though as I've never been able to divise a successful strategy around them even on their demo.