The Sonnar lens should work just fine on the Kiev....after all the Kiev cameras were made from the same tooling as the pre-war Contax cameras, with slight modifications as time went on, but the lens mount remained the same. You can also use Kiev lenses on your Contax cameras.
Now whether the Sonnar would be better is debateable. Since, in general, they are the same optical formula. The Sonnar would be manufactured to higher standards, but many people rave about the Jupiter ones. You may get a sub-standard Jupiter, or you may get an excellent one.
You can buy several Jupiter lenses for what you pay for one Sonnar. A newer coated Jupiter would probably be better than an older uncoated Sonnar.
In general all Contax and Kiev lenses freely interchange. The only caution here would be the Nikon RFDR mount lenses which, while mounting just fine, have focusing issues with Contax and Kiev RFDR cameras, unless you get a Nikon lens specifically made for Contax cameras, which are rather rare.