For time of the pocket pc years I was on Sprint, then went to ATT to get the iPhone 3G... then I returned to Sprint to get the EVO 4G.
In the pocket pc years, Sprint data was like to 2mb with the rev. in EVDO, happy days, also I had a data card for 2 years with them.
As a AT&T customer, the signal was really good and also the data, problem was the bill too high.
Right now, all the friends I bring to Sprint for the EVO 4G, are jumping back and others are on the fence to AT&T because of the slow data on Sprint.
If the're were no Network vision plans, i would jump to AT&T without thinking about it.
As two lines, I only think is if you need for work, do it, but if is just for fun, don't do it.