The currently active branches are 0.7.0 and 0.8.0. The master has been switched to tracking Apache Cassandra trunk. Current releases on the downloads section should be cosidered production ready. You should always choose the most recent release for your version of Apache Cassandra.
As of version 0.7.0-23, Hector artificats are deployed to Maven Central. If you use maven for your build system, you need only include the hector-core dependency and all related dependencies will be managed automatically.