This question depends on the size of your cluster specifically the number of endpoints you require.
If you are indending to have two separate device-pools and CCM groups in order to split the phones, and will be actively using both for CallProcessing then your options are limited between either.
What you also have to bear in mind is what other services you intend to activate across the cluster as well?
The simple reason is that there are certain caveats regarding service activation and when not to activate them.
For example the Media Streaming service, it stipulates that this service requires that you activate Cisco TFTP on one server in the cluster. Do not activate this service on the first node or on any servers that run the Cisco CallManager service.
Given your constraints you may find it pertinant to configure only a single CallManager group with the Subcriber and the Publisher in that order. Then enable the TFTP service, and the Media Service on the Publisher only, then the only dependency on the Publisher is when the Subcriber fails for call processing.
Regards
Allan.
