Verizon's CDMA is only CDMA on the download side. The upload is comparable to basic GPRS (about 56k). T-Mobile has recently upgraded their GPRS to the Edge GPRS standard. Although it's still GPRS, it does something with the timing in the radios at the cell towers which allows higher ul/dl speeds.

GPRS is the one that sacrifices speed for efficiency, although, I would personally go with the Verizon card.