I live in Gainesville, Florida so there is a lot of wifi downtown but i never go there so i would by the cingular wifi.
The AT&T Edge network (which runs off the cellular GSM signal) is the most complete "all over" network of it's kind in the country. Yes, there are faster networks, but the coverage is comparatively very small, and if you don't live inside a major metropolitan area, chances are that you cannot get connected anyway.
If you are looking for an internet iPod that can go just about anywhere, get the iPhone. If you are looking for an iPod that can access the internet wirelessly- where signals are available (and hopefully free) get the Touch.