I think when he says "full-keel", Sab30 is referring to the standard draft of that particular model boat he is looking at, as opposed to the shoal draft. He is comparing a newer shoal draft to a somewhat older standard draft of the same model.
Not knowing anything about the boat, my instinct would be to take the newer less costly shoal draft. But more info would be helpful. For instance if the shoal is a wing, I'd hesitate more. Also, if the shoal variant has less tankage, or has a reputation as a poor upwind sailor, all these factors would go into the equation.