Actually, Sprint now have the fastest network albeit in a very limited number of locations.
My experience is that, although HSDPA used by AT&T is theoretically faster than EVDO used by Verizon, in real life there's very little difference. If anything, Verizon is a little faster. As a very un-scientific test, using the speedtest.net app on my iphone gave me 784kbps down and 220 kpbs up. Using my Verizon Wireless card on my laptop (because AT&T wont let me use the iphone as a tethered modem - network capacity worries I guess), I got 822kbps down and 412kbps up. The difference is small enough to be effectively negligible. Both are fast enough for browsing / email and some low-grade file transfers. What I will say is that the Verizon wireless card will continue to give me those speeds is areas where the iPhone drops to Edge or GPRS.
Recent real world tests by several facilities say AT&T by far. The recent news named 3 or 4 companies /watchdogs that tested the systems. I believe it may still be up on CNN Tech News.
I can personally tell you that sprint is a terrible carrier as far as coverage. .
Quoted from CNN...
Analysts say AT&T's problems would have happened on any network that carried Apple's (AAPL, Fortune 500) iPhone because of the overwhelming amount of data downloaded by iPhone users. Over the past three years, AT&T's data traffic increased 5,000% because of the iPhone.
"There's a map for that" commercials have poked fun at AT&T's smaller 3G footprint. And that has helped Verizon take market share, according to Piper Jaffray.
But studies show that AT&T's network is actually faster than Verizon's, and Verizon's ad campaign may be a bit misleading.
Four recent independent studies from wireless industry analysis firms Global Wireless Solutions and Root Wireless, investment bank Piper Jaffray and tech blog Gizmodo all concluded that AT&T's 3G network was the fastest in the United States.
"We drove millions of miles across the country, and our data support AT&T's claim that it has the fastest 3G data network," said Global Wireless CEO Paul Carter.
The map that Verizon shows in its ads is correct, but AT&T's 3G network still covers nearly 80% of the U.S. population, said Carter. And AT&T's non-3G coverage is also broader than its 3G network.
With that kind of pedigree, analysts say AT&T was likely the best-equipped network to handle the iPhone.
"For Verizon ... we still wonder if the network has the capacity and backhaul to support a device with an adoption curve of the iPhone," said Piper Jaffray analyst Chris Larsen in a client note.
more....
http://money.cnn.com/2009/12/29/technology/att/index.htm?CNN=yes