We're a bit a hybrid of your scenarios. We have an SFDC user set up for system integrations anyway (SFDCAdmin), so that user is hooked into Marketo. I have an admin account as our primary SFDC Admin, our Sr. VP, Marketing has a near-full-admin account, and the remainder of the department shares a general Marketing SFDC login. The Marketing login has permission to view or edit pretty much any record, but is locked down from any admin functions.
There is no right and wrong answer. Just think about who needs to access what, who truly needsa a dedicated account for tracking and reporting, and go from there.