However it does depend on the amount of data you're talking about. Under 4GB (the maximum size USB memory the Xbox supports) if you have a known working USB memory device and don't already have a FTP set up in place I'd argue that on a level playing field it is faster (and easier) than any FTP alternative.
But you need good luck finding a 4GB or less USB memory device that functions properly with the Xbox though. It's very picky.
FTPing direct between two Xboxes ie. without a PC using the purpose designed Xbox FTP Client would seem like a good idea but in practice although it does work fine the, IMHO, inexplicably awkward controller GUI makes setting it up a very slow process. It might be better if you have a Xbox compatible keyboard but I can't comment on that.