According to this, AT&T is the fastest network, but I don't get anything near these speeds with my 9700. Whenever I try to open an attachment or whenever I am trying to stream a video/audio, it takes forever.. Even on BBM, when someone sends me a picture, it takes a while to download and open. When I mail some pictures same thing, although I can see upload speed is much slower.
If you compare this to older DSL services, it should open the attachments almost immediately.