It again comes down to what your purpose is for the email... if you're sending mass emails, the reporting is going to be a lot better via an email program. Likewise, if you want to set up a nurturing campaign, the engagement program will be the better fit from reporting, since that's its purpose.
For emails sent strictly through a smart campaign, I believe you'd have to generate an email performance report and set up some filters to ensure you're looking at just the emails sent from that campaign... basically it'd be a lot more work than the other ways.