iPhone Data Speeds On Different Networks - How Fast Are You Going?

I have a 4S on AT&T's wrongfully named 4G - which is really HSPA+.

In terms of real world performance I get around an average of 4 Mbps down and .9 going up. The highest speeds I have ever recorded on the Speedtest.net app are 6 down and 2 going up. I'm not too impressed.

My roommate's iPhone 5 on Sprint's 3G seems to fly, but I've heard people complain about their slow network. What are your experiences with AT&T, Sprint, Verizon, or T-Mobile?