I use six CZ Contax Yashica lenses, and have them on Leitax Sony A mounts. I always felt that Sony would do well, even back in a900 days, and I always like the colour more than C/N.
Now we have a camera and dream sensor to make them work great. I am lucky enough to be able to use an LA-EA3 maker's adapter. It works fine, weighs 110 grams and I figure not changing it out often means I can hopefully keep dust down to a workable level.
One thing that is surfacing with adapters is internal reflections, some users are getting strong flare, with the sun in/near the frame. I have heard that Novoflex is best of the non-Sony adapters.
The Contax lenses have their supporters, but most people think of them as 'not quite as good' predecessors to the ZEF range. They include some outrageous manual focus zooms that would never be made today. Aficionados however love them for the low contrast organic look, lighter weight, very good focus/aperture rings and across the frame sharpness at smaller apertures. On Sony a7r they are very appealing indeed. Mine average 18 years old.
Light ones that would work well:
18/4, 25/2.8, 28/2.8, 45/2.8, 50/1.4, 85/2.8, 100/3.5, all under 300-350 grams
many are around 475-600 grams: 21/2.8, 35-70/3.4, 135/2.8, 60/2.8 macro.
More (much more) fun information here from an unlikely source of Contax fans - RED users:
Contax Zeiss Survival Guide