I've tried Sprint 4G in a solid coverage area for a month (Vegas) and had no difference in speeds whatsoever. Returned the phone (evo).
In fact, I've gone in to the Sprint store and taken their demo units from the shelves and opened up speed testing websites and run them side by side with my 3G stuff and gotten the exact same speed.
Have repeated this a fee times. Their in store reps and phone reps just offer excuses about maybe the 4G tower being down (though you set the phone to connect to 4G only and it shows full signal strength), speeds fluctuate, etc. but none can explain why their 4G isn't faster.
This is about a mile from the strip, in super solid coverage on their maps.
So I don't bother anymore. Their 3G speed is okay. I'd rather have faster, but can't seem to get it.
I like Sprint a lot, but their 4G is terrible, IMO.