T-Mobile's data speeds were often twice as fast as second place AT&T. You can visit the sourcelink to see results of the speed tests in individual cities.
In the meantime, we can look at the results from some major cities. In Miami, on the download test, Verizon's 4G LTE just edged out T-Mobile's HSPA+ 42 pipeline, but those two were well above the rest of the carriers. On the upload side, Verizon's 4G LTE won by a landslide. In New York, it was AT&T's 4G LTE network that had the highest download speed which peaked at 41.59Mbps. Verizon's 4G LTE and T-Mobile's HSPA+ 42 had scores about half those of AT&T. Verizon's 4G LTE had the highest upload speeds. In San Francisco, it was AT&T's 4G LTE network that had the fastest download speeds while Verizon's 4G LTE pipeline offering the top upload speeds.
What about Sprint? Well, the carrier was at a disadvantage as it doesn't have an HSPA+ pipeline of course, and while it does offer 4G via WiMAX, those speeds are slower and later this year the carrier is expected to turn on its LTE network which means next year's tests should be more competitive.