I used the AT&T data card on a trial basis for a few weeks back in 2007, and the coverage at that time wasn't sufficient for what I was looking for west of the Illinois River, so
I returned it before the thirty day trial period expired. In the Macomb area, I dropped AT&T voice service shortly thereafter (I originally had AT&T/Cingular since I lived in North Central Illinois prior to emigrating here in 2003) due to very poor coverage; I can't speak as to what it's like presently.
I've been using Verizon's data service for two years, and in my own sanguine disposition, I am very satisfied with their coverage statewide. However, Verizon does not have mobile EVDO data coverage in a large area from roughly Shelbina, MO over into Adams County, IL and down to the Jacksonville and Pittsfield, IL areas, as this is primarily Sprint territory and it roams on 1XRTT. Essentially the southern half of the perceptual region "Forgottonia" (see map
http://upload.wikimedia.org/wikipedia/en/f/ff/Forgottonia_1972.PNG) has this issue with Verizon EVDO coverage.