3.0 is not backwards compatible. Whether to use 3.0 or 2.x depends upon the libraries you want to use. Some library writers are holding off the migration to 3.

3.0 is not backwards compatible. Whether to use 3.0 or 2.x depends upon the libraries you want to use. Some library writers are holding off the migration to 3.x until 3.0 is included as default in the popular linux distros.