First of all, let me preface this with the fact that this is my experience, so ymmv.
I tried it with tmobile 3G here in Orlando (the js won't do the tmo lte frequencies, iirc) and it was absolutely horrid. I've since moved it to at&t lte and it is obviously much faster, though, not quite as fast as my galaxy s3.
Hope that helps.
I'm up in Washington State, and service is great up here.
Most of the areas I frequent have the re-farmed 1900mhz PCS spectrum, so I've been able to use the Jetstream on cellular all the time.
I took a couple screenshots of what we're working with. I apologize in advance, the DPI isn't very forgiving using the SpeedTest app on the tablet.
The first is a screenshot of the cell info - showing that the JS is connected to T-Mobile's Network.
The second are the SpeedTest results on the Jetstream, on the 1900mhz network.
The third are the SpeedTest results on my GS3, on the 1700/2100mhz AWS network.