Data speeds depend on the connection, your computer processor, memory and where you are. Lots of variables and it isn't as cut and dried as cable/DSL at your home or office.
EV-DO (Verizon and Sprint) have the best high speed networks right now. They usually run from 750 kbps to 1.2 mbps with the next generation to go up to 3 mbps, if you believe the marketing hype. I carry a Verizon air card for my laptop with me all the time. $60 a month for unlimited data.
GSM (Cingular and T-Mobile) using EDGE is marketed at 70 to 235 kbps with the typical being 40-90 kbps - just a bit faster than dial up. 3G is hyped to be near broadband speeds, but the network is not as built out as Verizon' or Sprint's.
As for 6 months from now, your guess is as good as anyones. if you live, work, and pretty much stay in the Chicago area, I would assume any of the 3 you mention are fast. I think 3G is there. I know EV-Do is because I used it there in August.
