Being an Ex-Microsoft and My love for Microsoft Technology you will think I will be biased towards Dynamics CE, but here is what I would say, at the end of the day, our commonication with CRM is linked to Emails, almost all companies have outlook as email provider, with that said, Microsoft has best integration of email to Dynamics CRM, so at first shot I would select Dynamics CRM (of course at this point I am biased toward Microsoft).
In a situation like this, we can choose many cloud based products that are less dependent on customizations, more like less code soutions. We have HubSpot, ZohoCrm and many in the line. These are more geared towards marketing.
This is where all the heavy customization come in place, we can change the out of box process with Heavy plugin, workflow activities, custom actions, Lost more, we can even integrate CRM to LogicApps, Flows and custom connectors, and link to Azure.
In a situation like this, CRM is more like a platform, with lot of custom Tables (Entities) and data flowing in and out of the sytem, heavy integrations, now Dynamics CE becomes more like a platform than a product.
Heavy customization lot of data flow millions of records (Expensive) [go for SalesForce]
Heavy customization lot of data flow data within 5 millions of records (Cheap) [go for Dynamics CRM]
Would like to have good integration with other Microsoft Products. [go for Dynamics CRM]
Lot of documents to process, save, good case management [go for Dynamics CRM]
More marketing driven, less customications would like to use like directory [go for any, HubSpot, Zoho....]
Dynamics CE has the perfect Case management with integrated email system.
Dynamics CE has the perfect Unified Service Desk System, helps build perfect support floor.