I use BBTS and Toy Arena primarily. But my with my experience with them, I had no problems with TFSource. They have awesome customer service and their shipping of items is top notch.
TFSource and BBTS are your best bet for Online Transfomer or third party shopping. Either of the two are excellent. TFSource excels at customer service and the stated "bullet proof packaging." In my experience I've received everything I have ordered from them in two business days. It's lightning fast.