Fred, I have sprint for my phone, but I've used Verizon and ATT for data... I believe Sprint's data service charges are a lot higher, but I may be wrong.
I'm currently using ATT with a USB AirCard. I never had a problem on my last work laptop w/ the Verizon card, but at my current company we've had a rash of the PCMCIA slots going dead. (including my current laptop) The theory is the card getting bumped and messing up the connections on the main board, but I used to abuse my OLD laptop and never had aproblem w/ the PCMCIA slot
I just bought a new USB aircard off Ebay and popped my SIM card in it and I've been rolling ever since.
cool thing about it being USB is I can use it on pretty much ANY computer, even desktop units. Not that I have occasion to do that often, but it gives me a little backup on the home box if our cable connection goes down for whatever reason.
I've been happy with both Verizon and ATT data service