Sony's G lenses are large aperture optics which professional photographers use, and they are exceptionally helpful in low-light situations. The glass used, are of the highest quality and has minimal chromatic aberrations and distortion. As for Carl Zeiss lenses, they, too, offer high-quality lenses and have a rich heritage of designing optics for imaging purposes.
Igloo, I would suggest you check with those on-line sites and magazines that do independent review of photographic equipment to find a comparison of those lenses. I understand sony's alpha cameras can use both CZ and G lenses, so someone must have tested both. I wouldn't expect to get an unbiased view of sony's products on this forum. E.g. "SonyMod_wi" sounds like a Sony apologist to me - no real info in their response to your question. I suspect the choice of Sony to switch from CZ lenses to Sony was just an economic choice to bring the lens production in-house with the savings and control that affords a large company. Good luck! Would be interesting if you would post whatever you find back on this site.