CAs cannot be updated, nor deleted. COs can. So CAs are not good for business information that need such updates or deletion.
On the other end, CAs cannot be tempered with, which is an advantage if you are in compliance situation
CAs cannot be imported, they are only created though API calls
COs can have text fields, CAs cannot. If you need to store long data, that may make a difference.
With regards to triggering, the 2 are very similar. If you are on Orion, you can ask your CSM to get a custom object update trigger that can be essential for some activities.
With regards to filtering, COs are superior with 2 filters ("Has CO" and "Was added to CO"), vs one for CAs. CO filters enable you to filter on current or passed situations.