Are Sony G lenses or Zeiss Lenses worth it?

Yes,I have an a-100 and G lenses are excellant! Go to lens rentals and rent the 70-400mm G lens. You won't want to use anything else!

I recommend the Sony Zeiss lenses.The mechanical construction of the lenses is excellent. They all have satin black metal barrels with textured rubber grip surfaces. Since they are all manual focus lenses, the focusing action is firm and smooth. The feeling is much different than manually focusing most AF lenses. Since there is no concern about a small motor having to do the work, a substantial damping can be applied. All of the lenses look the same - that is to say, they all have the same finish, the same texture, the same design and the same layout. The engraving and finish quality is outstanding. I am very picky about such things, and these lenses impress me. Occasionally, the Kyocera quality control lets a bad one slip through. I have sent back two of them for defects - one substantial and one trivial. The sturdiness of the Contax lens mounts / camera coupling connectors have sometimes been called into question. They are not as rugged as the Leica or Canon mounts and banging them about can result is misalignment. They are very secure on the camera. The problem comes when left unprotected off the camera. The aperture rings are smooth but do not use ball bearings like the even smoother Leica lenses.

There are two types of Zeiss / Contax lenses - MM and AE. The MM lenses fully support all camera functions, including manual, program, aperture priority and shutter speed priority modes. The AE lenses lack the mechanism that allows the camera body to control the aperture diaphragm in the lens. Accordingly, AE lenses do not function in program or shutter priority modes. Zeiss has gradually been eliminating AE lenses. Only certain specialty lenses are available as AE. The great majority are now all MM lenses.

Now for the real meat - the optical quality. These lenses are excellent - almost uniformly. While some are better than others, there are no "consumer grade" and no poor performers that I have used.

By the way, if you are not aware of this, they are "licensed" by Sony and made in Japan, if you are really into "Carl Zeiss of Germany" label.

Leitz / Leica did the same with Panasonic.

Definitely Zeiss!

zeiss makes excelent optics, and i do believe that they make autofocus lenses for the sony mount,

their nikon and canon mount lenses are manual focus.