Both work in slightly different ways so it really depends on what you are after.
The Cybershot range which have Sweep Panorama record the image as a movie and then take a slice of each image to create the final result.
3D stills however work without the sweep motion taking 2 images one after another focusing at various depths so in theory creating a higher resolution image, BUT more prone to blur from camera shake since it takes a bit longer.
Best thing before considering the upgrade is take your Memory Stick/SD down to a dealer who has one of the newer models and take a few pictures. Then you can go home and compare.
In all honesty, even thought Sweep Panoramic models record as a movie then slice it up, the differences in the real world are not that different.
Hope that helps.