You should use the most recent version of the model that is available unless you are trying to replicate previous results or create a branch run from a previous experiment.
|CESM2 Release Versions
|CESM1 Release Versions
Scientifically Validated Configurations
Scientific validation of the CESM consists of a multi-decadal model run of the given component set at the target resolution, followed by scientific review of the model output diagnostics. All scientifically supported component sets are also accompanied by diagnostic and model output data.
CESM 2.0 is in the process of adding scientically validated configurations and these will be posted on the web site as they become available.
The DiscussCESM Forums bulletin board can also provide specific recommendations from the CESM community regarding which release of the model to use for your specific requirements.