Case Comments vs. Chatter Feed
Case Comments are to be reserved and to be available for all those who see the case, it's meant for more important things AND for the owner of the case mostly.
Chatter is nice to have when co-workers are to interact and advise each other on that case. Or, for the case owner to notify his/her manager about a special issue hapenning on that specific case.
So, I would say, you would want to use both. Case owners are to record their information on case comments. External ineractions with users other than the owner can be chattered.
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