The best network in the US that I have seen is the new 3G service from AT&T - which is as fast as basic DSL speeds (1.2Mb/s down, 650kb/s up) and has almost no noticeable latency that I could really see. My father has a wireless card for his laptop and it's really impressive - it feels almost as fast as using WiFi on cable modem connection. You can bring up the Yahoo homepage in about a second.
The next best is Sprint and Verizon with EVDO. Sprint is on EVDO rev.A and is usually somewhere around 900kb/s down and 500kB/s up) while Verizon is on EVDO rev.0 and is 800kb/s down, 120kb/s up. It has a much more noticeable latency than AT&T's 3G, but it still a pretty reasonable browsing experience. My mother has a wireless EVDO card on Verizon and bringing up the Yahoo homepage takes about 5 seconds but fees a bit laggy.
Below that is EDGE on T-Mobile and AT&T (for AT&T areas without 3G - which is most of the US). It has a significant amount of latency and bandwidth is around ~140kb/s down and about ~10kb/s up. I have EDGE on T-Mobile and I can pull up the Yahoo home page in about 15 seconds and feels very slow.
All of these assume excellent radio coverage... if you only have one bar worth of reception, even 3G is pretty slow... and EDGE is so slow that pages usually time out. I haven't actually tried running ping on any of the above - but I have spent some time browsing on my Dad's 3G and my Mom's Verizon EVDO and a ton of time browsing on my home cable modem and my T-Mobile EDGE and I can say that 3G feels very close to a "real" internet connection. It's slightly laggier and a bit slower... but it feels "fast". But a lot of areas don't have 3G AT&T yet... in which case you are back stuck with EDGE again. If you aren't in an AT&T 3G area, or you travel a lot, then Sprint is your next best bet.