We went through a similar exercise a while ago and decided to keep it simple i.e. a) If an email isn't going to drive demand (e.g. some of our e-newsletters, product updates, all internal communications) then we use e-Marketeer and; b) For small email sends, e.g. to a small number of our sales partners owned by the particular Sales/Channel Account Manager in SFDC, then Sales can use SFDC. Everything else is built in Marketo because of the better features for analytics, reporting, and design etc. In our case only Marketing and Corporate Communications issue emails in large batches - Sales don't have the access and have to brief Marketing.
... View more