I had to pickup a Sprint Overdrive 4g/3g card for work recently and put the two networks head to head using Speedtest.net. Here are the visual results:

Sprint 4G

Sprint 4G (Test #2)

AT&T 3G
![AT&T 3G [Test #2]](http://i.imgur.com/VCCNC.png)
AT&T 3G [Test #2
Sprint: $60/mo for unlimited 4g, 5gb of 3g.
AT&T: +$20/mo for tethering, unlimited if grandfathered in [source].
The real test will be reliability and whether or not the AT&T / iOS tethering actually happens.
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