The latest stable Python release is 1.2.4 (https://pypi.python.org/pypi/couchbase), though anything within the 1.2.x series should be very stable.
The latest libcouchbase release is 2.4.3, though likewise, the 2.4.x series is fairly stable.
There’s a compatibility matrix in our documentation (at least for the C library) which shows which features are supported on which client and server, but this feature matrix is limited to the specific features which require coordination between both client and server. Most of the features of Couchbase are typically independent of the client, unless they expose APIs directly to the application: